diff --git a/gucc/include/gucc/locale.hpp b/gucc/include/gucc/locale.hpp
index 02efd48..67766d3 100644
--- a/gucc/include/gucc/locale.hpp
+++ b/gucc/include/gucc/locale.hpp
@@ -8,6 +8,10 @@ namespace gucc::locale {
 // Set system language
 auto set_locale(std::string_view locale, std::string_view mountpoint) noexcept -> bool;
 
+// Prepare system language.
+// Sets without updating system locale
+auto prepare_locale_set(std::string_view locale, std::string_view mountpoint) noexcept -> bool;
+
 }  // namespace gucc::locale
 
 #endif  // LOCALE_HPP
diff --git a/gucc/src/locale.cpp b/gucc/src/locale.cpp
index cc408d6..9e9c5f9 100644
--- a/gucc/src/locale.cpp
+++ b/gucc/src/locale.cpp
@@ -12,7 +12,7 @@ using namespace std::string_view_literals;
 
 namespace gucc::locale {
 
-auto set_locale(std::string_view locale, std::string_view mountpoint) noexcept -> bool {
+auto prepare_locale_set(std::string_view locale, std::string_view mountpoint) noexcept -> bool {
     const auto& locale_config_path = fmt::format(FMT_COMPILE("{}/etc/locale.conf"), mountpoint);
     const auto& locale_gen_path    = fmt::format(FMT_COMPILE("{}/etc/locale.gen"), mountpoint);
 
@@ -40,13 +40,23 @@ LC_MESSAGES="{0}"
     // TODO(vnepogodin): refactor and make backups of locale config and locale gen
     utils::exec(fmt::format(FMT_COMPILE("sed -i \"s/#{0}/{0}/\" {1}"), locale, locale_gen_path));
 
+    // NOTE: maybe we should also write into /etc/default/locale if /etc/default exists and is a dir?
+    return true;
+}
+
+auto set_locale(std::string_view locale, std::string_view mountpoint) noexcept -> bool {
+    // Prepare locale
+    if (!locale::prepare_locale_set(locale, mountpoint)) {
+        spdlog::error("Failed to prepare locale files for '{}'", locale);
+        return false;
+    }
+
     // Generate locales
     if (!utils::arch_chroot_checked("locale-gen", mountpoint)) {
         spdlog::error("Failed to run locale-gen with locale '{}'", locale);
         return false;
     }
 
-    // NOTE: maybe we should also write into /etc/default/locale if /etc/default exists and is a dir?
     return true;
 }
 
diff --git a/gucc/tests/CMakeLists.txt b/gucc/tests/CMakeLists.txt
index fd93df1..63d7f63 100644
--- a/gucc/tests/CMakeLists.txt
+++ b/gucc/tests/CMakeLists.txt
@@ -4,6 +4,8 @@
 
 file(GLOB files unit-*.cpp)
 
+set(GUCC_TEST_DIR "${CMAKE_CURRENT_SOURCE_DIR}/")
+
 foreach(file ${files})
     get_filename_component(file_basename ${file} NAME_WE)
     string(REGEX REPLACE "unit-([^$]+)" "test-\\1" testcase ${file_basename})
@@ -13,5 +15,6 @@ foreach(file ${files})
         $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated;-Wno-float-equal>
         $<$<CXX_COMPILER_ID:GNU>:-Wno-deprecated-declarations>
     )
+    add_definitions(-DGUCC_TEST_DIR="${GUCC_TEST_DIR}")
     target_link_libraries(${testcase} PRIVATE project_warnings project_options gucc::gucc)
 endforeach()
diff --git a/gucc/tests/files/locale.gen b/gucc/tests/files/locale.gen
new file mode 100644
index 0000000..c5476c5
--- /dev/null
+++ b/gucc/tests/files/locale.gen
@@ -0,0 +1,512 @@
+# Configuration file for locale-gen
+#
+# lists of locales that are to be generated by the locale-gen command.
+#
+# Each line is of the form:
+#
+#     <locale> <charset>
+#
+#  where <locale> is one of the locales given in /usr/share/i18n/locales
+#  and <charset> is one of the character sets listed in /usr/share/i18n/charmaps
+#
+#  Examples:
+#  en_US ISO-8859-1
+#  en_US.UTF-8 UTF-8
+#  de_DE ISO-8859-1
+#  de_DE@euro ISO-8859-15
+#
+#  The locale-gen command will generate all the locales,
+#  placing them in /usr/lib/locale.
+#
+#  A list of supported locales is included in this file.
+#  Uncomment the ones you need.
+#
+#aa_DJ.UTF-8 UTF-8
+#aa_DJ ISO-8859-1
+#aa_ER UTF-8
+#aa_ER@saaho UTF-8
+#aa_ET UTF-8
+#af_ZA.UTF-8 UTF-8
+#af_ZA ISO-8859-1
+#agr_PE UTF-8
+#ak_GH UTF-8
+#am_ET UTF-8
+#an_ES.UTF-8 UTF-8
+#an_ES ISO-8859-15
+#anp_IN UTF-8
+#ar_AE.UTF-8 UTF-8
+#ar_AE ISO-8859-6
+#ar_BH.UTF-8 UTF-8
+#ar_BH ISO-8859-6
+#ar_DZ.UTF-8 UTF-8
+#ar_DZ ISO-8859-6
+#ar_EG.UTF-8 UTF-8
+#ar_EG ISO-8859-6
+#ar_IN UTF-8
+#ar_IQ.UTF-8 UTF-8
+#ar_IQ ISO-8859-6
+#ar_JO.UTF-8 UTF-8
+#ar_JO ISO-8859-6
+#ar_KW.UTF-8 UTF-8
+#ar_KW ISO-8859-6
+#ar_LB.UTF-8 UTF-8
+#ar_LB ISO-8859-6
+#ar_LY.UTF-8 UTF-8
+#ar_LY ISO-8859-6
+#ar_MA.UTF-8 UTF-8
+#ar_MA ISO-8859-6
+#ar_OM.UTF-8 UTF-8
+#ar_OM ISO-8859-6
+#ar_QA.UTF-8 UTF-8
+#ar_QA ISO-8859-6
+#ar_SA.UTF-8 UTF-8
+#ar_SA ISO-8859-6
+#ar_SD.UTF-8 UTF-8
+#ar_SD ISO-8859-6
+#ar_SS UTF-8
+#ar_SY.UTF-8 UTF-8
+#ar_SY ISO-8859-6
+#ar_TN.UTF-8 UTF-8
+#ar_TN ISO-8859-6
+#ar_YE.UTF-8 UTF-8
+#ar_YE ISO-8859-6
+#ayc_PE UTF-8
+#az_AZ UTF-8
+#az_IR UTF-8
+#as_IN UTF-8
+#ast_ES.UTF-8 UTF-8
+#ast_ES ISO-8859-15
+#be_BY.UTF-8 UTF-8
+#be_BY CP1251
+#be_BY@latin UTF-8
+#bem_ZM UTF-8
+#ber_DZ UTF-8
+#ber_MA UTF-8
+#bg_BG.UTF-8 UTF-8
+#bg_BG CP1251
+#bhb_IN.UTF-8 UTF-8
+#bho_IN UTF-8
+#bho_NP UTF-8
+#bi_VU UTF-8
+#bn_BD UTF-8
+#bn_IN UTF-8
+#bo_CN UTF-8
+#bo_IN UTF-8
+#br_FR.UTF-8 UTF-8
+#br_FR ISO-8859-1
+#br_FR@euro ISO-8859-15
+#brx_IN UTF-8
+#bs_BA.UTF-8 UTF-8
+#bs_BA ISO-8859-2
+#byn_ER UTF-8
+#C.UTF-8 UTF-8
+#ca_AD.UTF-8 UTF-8
+#ca_AD ISO-8859-15
+#ca_ES.UTF-8 UTF-8
+#ca_ES ISO-8859-1
+#ca_ES@euro ISO-8859-15
+#ca_ES@valencia UTF-8
+#ca_FR.UTF-8 UTF-8
+#ca_FR ISO-8859-15
+#ca_IT.UTF-8 UTF-8
+#ca_IT ISO-8859-15
+#ce_RU UTF-8
+#chr_US UTF-8
+#ckb_IQ UTF-8
+#cmn_TW UTF-8
+#crh_UA UTF-8
+#cs_CZ.UTF-8 UTF-8
+#cs_CZ ISO-8859-2
+#csb_PL UTF-8
+#cv_RU UTF-8
+#cy_GB.UTF-8 UTF-8
+#cy_GB ISO-8859-14
+#da_DK.UTF-8 UTF-8
+#da_DK ISO-8859-1
+#de_AT.UTF-8 UTF-8
+#de_AT ISO-8859-1
+#de_AT@euro ISO-8859-15
+#de_BE.UTF-8 UTF-8
+#de_BE ISO-8859-1
+#de_BE@euro ISO-8859-15
+#de_CH.UTF-8 UTF-8
+#de_CH ISO-8859-1
+#de_DE.UTF-8 UTF-8
+#de_DE ISO-8859-1
+#de_DE@euro ISO-8859-15
+#de_IT.UTF-8 UTF-8
+#de_IT ISO-8859-1
+#de_LI.UTF-8 UTF-8
+#de_LU.UTF-8 UTF-8
+#de_LU ISO-8859-1
+#de_LU@euro ISO-8859-15
+#doi_IN UTF-8
+#dsb_DE UTF-8
+#dv_MV UTF-8
+#dz_BT UTF-8
+#el_GR.UTF-8 UTF-8
+#el_GR ISO-8859-7
+#el_GR@euro ISO-8859-7
+#el_CY.UTF-8 UTF-8
+#el_CY ISO-8859-7
+#en_AG UTF-8
+#en_AU.UTF-8 UTF-8
+#en_AU ISO-8859-1
+#en_BW.UTF-8 UTF-8
+#en_BW ISO-8859-1
+#en_CA.UTF-8 UTF-8
+#en_CA ISO-8859-1
+#en_DK.UTF-8 UTF-8
+#en_DK ISO-8859-1
+#en_GB.UTF-8 UTF-8
+#en_GB ISO-8859-1
+#en_HK.UTF-8 UTF-8
+#en_HK ISO-8859-1
+#en_IE.UTF-8 UTF-8
+#en_IE ISO-8859-1
+#en_IE@euro ISO-8859-15
+#en_IL UTF-8
+#en_IN UTF-8
+#en_NG UTF-8
+#en_NZ.UTF-8 UTF-8
+#en_NZ ISO-8859-1
+#en_PH.UTF-8 UTF-8
+#en_PH ISO-8859-1
+#en_SC.UTF-8 UTF-8
+#en_SG.UTF-8 UTF-8
+#en_SG ISO-8859-1
+#en_US.UTF-8 UTF-8
+#en_US ISO-8859-1
+#en_ZA.UTF-8 UTF-8
+#en_ZA ISO-8859-1
+#en_ZM UTF-8
+#en_ZW.UTF-8 UTF-8
+#en_ZW ISO-8859-1
+#eo UTF-8
+#es_AR.UTF-8 UTF-8
+#es_AR ISO-8859-1
+#es_BO.UTF-8 UTF-8
+#es_BO ISO-8859-1
+#es_CL.UTF-8 UTF-8
+#es_CL ISO-8859-1
+#es_CO.UTF-8 UTF-8
+#es_CO ISO-8859-1
+#es_CR.UTF-8 UTF-8
+#es_CR ISO-8859-1
+#es_CU UTF-8
+#es_DO.UTF-8 UTF-8
+#es_DO ISO-8859-1
+#es_EC.UTF-8 UTF-8
+#es_EC ISO-8859-1
+#es_ES.UTF-8 UTF-8
+#es_ES ISO-8859-1
+#es_ES@euro ISO-8859-15
+#es_GT.UTF-8 UTF-8
+#es_GT ISO-8859-1
+#es_HN.UTF-8 UTF-8
+#es_HN ISO-8859-1
+#es_MX.UTF-8 UTF-8
+#es_MX ISO-8859-1
+#es_NI.UTF-8 UTF-8
+#es_NI ISO-8859-1
+#es_PA.UTF-8 UTF-8
+#es_PA ISO-8859-1
+#es_PE.UTF-8 UTF-8
+#es_PE ISO-8859-1
+#es_PR.UTF-8 UTF-8
+#es_PR ISO-8859-1
+#es_PY.UTF-8 UTF-8
+#es_PY ISO-8859-1
+#es_SV.UTF-8 UTF-8
+#es_SV ISO-8859-1
+#es_US.UTF-8 UTF-8
+#es_US ISO-8859-1
+#es_UY.UTF-8 UTF-8
+#es_UY ISO-8859-1
+#es_VE.UTF-8 UTF-8
+#es_VE ISO-8859-1
+#et_EE.UTF-8 UTF-8
+#et_EE ISO-8859-1
+#et_EE.ISO-8859-15 ISO-8859-15
+#eu_ES.UTF-8 UTF-8
+#eu_ES ISO-8859-1
+#eu_ES@euro ISO-8859-15
+#fa_IR UTF-8
+#ff_SN UTF-8
+#fi_FI.UTF-8 UTF-8
+#fi_FI ISO-8859-1
+#fi_FI@euro ISO-8859-15
+#fil_PH UTF-8
+#fo_FO.UTF-8 UTF-8
+#fo_FO ISO-8859-1
+#fr_BE.UTF-8 UTF-8
+#fr_BE ISO-8859-1
+#fr_BE@euro ISO-8859-15
+#fr_CA.UTF-8 UTF-8
+#fr_CA ISO-8859-1
+#fr_CH.UTF-8 UTF-8
+#fr_CH ISO-8859-1
+#fr_FR.UTF-8 UTF-8
+#fr_FR ISO-8859-1
+#fr_FR@euro ISO-8859-15
+#fr_LU.UTF-8 UTF-8
+#fr_LU ISO-8859-1
+#fr_LU@euro ISO-8859-15
+#fur_IT UTF-8
+#fy_NL UTF-8
+#fy_DE UTF-8
+#ga_IE.UTF-8 UTF-8
+#ga_IE ISO-8859-1
+#ga_IE@euro ISO-8859-15
+#gd_GB.UTF-8 UTF-8
+#gd_GB ISO-8859-15
+#gez_ER UTF-8
+#gez_ER@abegede UTF-8
+#gez_ET UTF-8
+#gez_ET@abegede UTF-8
+#gl_ES.UTF-8 UTF-8
+#gl_ES ISO-8859-1
+#gl_ES@euro ISO-8859-15
+#gu_IN UTF-8
+#gv_GB.UTF-8 UTF-8
+#gv_GB ISO-8859-1
+#ha_NG UTF-8
+#hak_TW UTF-8
+#he_IL.UTF-8 UTF-8
+#he_IL ISO-8859-8
+#hi_IN UTF-8
+#hif_FJ UTF-8
+#hne_IN UTF-8
+#hr_HR.UTF-8 UTF-8
+#hr_HR ISO-8859-2
+#hsb_DE ISO-8859-2
+#hsb_DE.UTF-8 UTF-8
+#ht_HT UTF-8
+#hu_HU.UTF-8 UTF-8
+#hu_HU ISO-8859-2
+#hy_AM UTF-8
+#hy_AM.ARMSCII-8 ARMSCII-8
+#ia_FR UTF-8
+#id_ID.UTF-8 UTF-8
+#id_ID ISO-8859-1
+#ig_NG UTF-8
+#ik_CA UTF-8
+#is_IS.UTF-8 UTF-8
+#is_IS ISO-8859-1
+#it_CH.UTF-8 UTF-8
+#it_CH ISO-8859-1
+#it_IT.UTF-8 UTF-8
+#it_IT ISO-8859-1
+#it_IT@euro ISO-8859-15
+#iu_CA UTF-8
+#ja_JP.EUC-JP EUC-JP
+#ja_JP.UTF-8 UTF-8
+#ka_GE.UTF-8 UTF-8
+#ka_GE GEORGIAN-PS
+#kab_DZ UTF-8
+#kk_KZ.UTF-8 UTF-8
+#kk_KZ PT154
+#kl_GL.UTF-8 UTF-8
+#kl_GL ISO-8859-1
+#km_KH UTF-8
+#kn_IN UTF-8
+#ko_KR.EUC-KR EUC-KR
+#ko_KR.UTF-8 UTF-8
+#kok_IN UTF-8
+#ks_IN UTF-8
+#ks_IN@devanagari UTF-8
+#ku_TR.UTF-8 UTF-8
+#ku_TR ISO-8859-9
+#kw_GB.UTF-8 UTF-8
+#kw_GB ISO-8859-1
+#ky_KG UTF-8
+#lb_LU UTF-8
+#lg_UG.UTF-8 UTF-8
+#lg_UG ISO-8859-10
+#li_BE UTF-8
+#li_NL UTF-8
+#lij_IT UTF-8
+#ln_CD UTF-8
+#lo_LA UTF-8
+#lt_LT.UTF-8 UTF-8
+#lt_LT ISO-8859-13
+#lv_LV.UTF-8 UTF-8
+#lv_LV ISO-8859-13
+#lzh_TW UTF-8
+#mag_IN UTF-8
+#mai_IN UTF-8
+#mai_NP UTF-8
+#mfe_MU UTF-8
+#mg_MG.UTF-8 UTF-8
+#mg_MG ISO-8859-15
+#mhr_RU UTF-8
+#mi_NZ.UTF-8 UTF-8
+#mi_NZ ISO-8859-13
+#miq_NI UTF-8
+#mjw_IN UTF-8
+#mk_MK.UTF-8 UTF-8
+#mk_MK ISO-8859-5
+#ml_IN UTF-8
+#mn_MN UTF-8
+#mni_IN UTF-8
+#mnw_MM UTF-8
+#mr_IN UTF-8
+#ms_MY.UTF-8 UTF-8
+#ms_MY ISO-8859-1
+#mt_MT.UTF-8 UTF-8
+#mt_MT ISO-8859-3
+#my_MM UTF-8
+#nan_TW UTF-8
+#nan_TW@latin UTF-8
+#nb_NO.UTF-8 UTF-8
+#nb_NO ISO-8859-1
+#nds_DE UTF-8
+#nds_NL UTF-8
+#ne_NP UTF-8
+#nhn_MX UTF-8
+#niu_NU UTF-8
+#niu_NZ UTF-8
+#nl_AW UTF-8
+#nl_BE.UTF-8 UTF-8
+#nl_BE ISO-8859-1
+#nl_BE@euro ISO-8859-15
+#nl_NL.UTF-8 UTF-8
+#nl_NL ISO-8859-1
+#nl_NL@euro ISO-8859-15
+#nn_NO.UTF-8 UTF-8
+#nn_NO ISO-8859-1
+#nr_ZA UTF-8
+#nso_ZA UTF-8
+#oc_FR.UTF-8 UTF-8
+#oc_FR ISO-8859-1
+#om_ET UTF-8
+#om_KE.UTF-8 UTF-8
+#om_KE ISO-8859-1
+#or_IN UTF-8
+#os_RU UTF-8
+#pa_IN UTF-8
+#pa_PK UTF-8
+#pap_AW UTF-8
+#pap_CW UTF-8
+#pl_PL.UTF-8 UTF-8
+#pl_PL ISO-8859-2
+#ps_AF UTF-8
+#pt_BR.UTF-8 UTF-8
+#pt_BR ISO-8859-1
+#pt_PT.UTF-8 UTF-8
+#pt_PT ISO-8859-1
+#pt_PT@euro ISO-8859-15
+#quz_PE UTF-8
+#raj_IN UTF-8
+#ro_RO.UTF-8 UTF-8
+#ro_RO ISO-8859-2
+#ru_RU.KOI8-R KOI8-R
+#ru_RU.UTF-8 UTF-8
+#ru_RU ISO-8859-5
+#ru_UA.UTF-8 UTF-8
+#ru_UA KOI8-U
+#rw_RW UTF-8
+#sa_IN UTF-8
+#sah_RU UTF-8
+#sat_IN UTF-8
+#sc_IT UTF-8
+#sd_IN UTF-8
+#sd_IN@devanagari UTF-8
+#se_NO UTF-8
+#sgs_LT UTF-8
+#shn_MM UTF-8
+#shs_CA UTF-8
+#si_LK UTF-8
+#sid_ET UTF-8
+#sk_SK.UTF-8 UTF-8
+#sk_SK ISO-8859-2
+#sl_SI.UTF-8 UTF-8
+#sl_SI ISO-8859-2
+#sm_WS UTF-8
+#so_DJ.UTF-8 UTF-8
+#so_DJ ISO-8859-1
+#so_ET UTF-8
+#so_KE.UTF-8 UTF-8
+#so_KE ISO-8859-1
+#so_SO.UTF-8 UTF-8
+#so_SO ISO-8859-1
+#sq_AL.UTF-8 UTF-8
+#sq_AL ISO-8859-1
+#sq_MK UTF-8
+#sr_ME UTF-8
+#sr_RS UTF-8
+#sr_RS@latin UTF-8
+#ss_ZA UTF-8
+#st_ZA.UTF-8 UTF-8
+#st_ZA ISO-8859-1
+#sv_FI.UTF-8 UTF-8
+#sv_FI ISO-8859-1
+#sv_FI@euro ISO-8859-15
+#sv_SE.UTF-8 UTF-8
+#sv_SE ISO-8859-1
+#sw_KE UTF-8
+#sw_TZ UTF-8
+#szl_PL UTF-8
+#ta_IN UTF-8
+#ta_LK UTF-8
+#tcy_IN.UTF-8 UTF-8
+#te_IN UTF-8
+#tg_TJ.UTF-8 UTF-8
+#tg_TJ KOI8-T
+#th_TH.UTF-8 UTF-8
+#th_TH TIS-620
+#the_NP UTF-8
+#ti_ER UTF-8
+#ti_ET UTF-8
+#tig_ER UTF-8
+#tk_TM UTF-8
+#tl_PH.UTF-8 UTF-8
+#tl_PH ISO-8859-1
+#tn_ZA UTF-8
+#to_TO UTF-8
+#tpi_PG UTF-8
+#tr_CY.UTF-8 UTF-8
+#tr_CY ISO-8859-9
+#tr_TR.UTF-8 UTF-8
+#tr_TR ISO-8859-9
+#ts_ZA UTF-8
+#tt_RU UTF-8
+#tt_RU@iqtelif UTF-8
+#ug_CN UTF-8
+#uk_UA.UTF-8 UTF-8
+#uk_UA KOI8-U
+#unm_US UTF-8
+#ur_IN UTF-8
+#ur_PK UTF-8
+#uz_UZ.UTF-8 UTF-8
+#uz_UZ ISO-8859-1
+#uz_UZ@cyrillic UTF-8
+#ve_ZA UTF-8
+#vi_VN UTF-8
+#wa_BE ISO-8859-1
+#wa_BE@euro ISO-8859-15
+#wa_BE.UTF-8 UTF-8
+#wae_CH UTF-8
+#wal_ET UTF-8
+#wo_SN UTF-8
+#xh_ZA.UTF-8 UTF-8
+#xh_ZA ISO-8859-1
+#yi_US.UTF-8 UTF-8
+#yi_US CP1255
+#yo_NG UTF-8
+#yue_HK UTF-8
+#yuw_PG UTF-8
+#zh_CN.GB18030 GB18030
+#zh_CN.GBK GBK
+#zh_CN.UTF-8 UTF-8
+#zh_CN GB2312
+#zh_HK.UTF-8 UTF-8
+#zh_HK BIG5-HKSCS
+#zh_SG.UTF-8 UTF-8
+#zh_SG.GBK GBK
+#zh_SG GB2312
+#zh_TW.EUC-TW EUC-TW
+#zh_TW.UTF-8 UTF-8
+#zh_TW BIG5
+#zu_ZA.UTF-8 UTF-8
+#zu_ZA ISO-8859-1
diff --git a/gucc/tests/meson.build b/gucc/tests/meson.build
index 316037c..7ffbb2c 100644
--- a/gucc/tests/meson.build
+++ b/gucc/tests/meson.build
@@ -1,3 +1,6 @@
+# gucc test path
+add_global_arguments('-DGUCC_TEST_DIR="' + meson.current_source_dir() + '"', language : 'cpp')
+
 executable(
   'test-initcpio',
   files('unit-initcpio.cpp'),
@@ -45,3 +48,11 @@ executable(
   link_with: [gucc_lib],
   include_directories: [include_directories('../include')],
   install: false)
+
+executable(
+  'test-locale',
+  files('unit-locale.cpp'),
+  dependencies: deps,
+  link_with: [gucc_lib],
+  include_directories: [include_directories('../include')],
+  install: false)
diff --git a/gucc/tests/unit-locale.cpp b/gucc/tests/unit-locale.cpp
new file mode 100644
index 0000000..539b56c
--- /dev/null
+++ b/gucc/tests/unit-locale.cpp
@@ -0,0 +1,95 @@
+#include "gucc/file_utils.hpp"
+#include "gucc/locale.hpp"
+
+#include <cassert>
+
+#include <filesystem>
+#include <fstream>
+#include <string_view>
+
+#include <fmt/core.h>
+
+#include <spdlog/sinks/callback_sink.h>
+#include <spdlog/spdlog.h>
+
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wold-style-cast"
+#elif defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnull-dereference"
+#pragma GCC diagnostic ignored "-Wuseless-cast"
+#pragma GCC diagnostic ignored "-Wold-style-cast"
+#endif
+
+#include <range/v3/range/conversion.hpp>
+#include <range/v3/view/filter.hpp>
+#include <range/v3/view/join.hpp>
+#include <range/v3/view/split.hpp>
+
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
+
+namespace fs = std::filesystem;
+using namespace std::string_view_literals;
+
+static constexpr auto LOCALE_CONF_TEST = R"(LANG="ru_RU.UTF-8"
+LC_NUMERIC="ru_RU.UTF-8"
+LC_TIME="ru_RU.UTF-8"
+LC_MONETARY="ru_RU.UTF-8"
+LC_PAPER="ru_RU.UTF-8"
+LC_NAME="ru_RU.UTF-8"
+LC_ADDRESS="ru_RU.UTF-8"
+LC_TELEPHONE="ru_RU.UTF-8"
+LC_MEASUREMENT="ru_RU.UTF-8"
+LC_IDENTIFICATION="ru_RU.UTF-8"
+LC_MESSAGES="ru_RU.UTF-8"
+)"sv;
+
+static constexpr auto LOCALE_GEN_TEST = R"(ru_RU.UTF-8 UTF-8
+)"sv;
+
+inline auto filtered_res(std::string_view content) noexcept -> std::string {
+    auto&& result = content | ranges::views::split('\n')
+        | ranges::views::filter([](auto&& rng) {
+              auto&& line = std::string_view(&*rng.begin(), static_cast<size_t>(ranges::distance(rng)));
+              return !line.empty() && !line.starts_with('#');
+          })
+        | ranges::views::join('\n')
+        | ranges::to<std::string>();
+    return result + '\n';
+}
+
+int main() {
+    auto callback_sink = std::make_shared<spdlog::sinks::callback_sink_mt>([](const spdlog::details::log_msg&) {
+        // noop
+    });
+    spdlog::set_default_logger(std::make_shared<spdlog::logger>("default", callback_sink));
+
+    // prepare test data
+    static constexpr std::string_view folder_testpath{"/tmp/test-locale-unittest"};
+    static constexpr std::string_view folder_path{"/tmp/test-locale-unittest/etc"};
+    static constexpr std::string_view dest_locale_gen{"/tmp/test-locale-unittest/etc/locale.gen"};
+    static constexpr std::string_view dest_locale_conf{"/tmp/test-locale-unittest/etc/locale.conf"};
+
+    fs::create_directories(folder_path);
+
+    fs::copy_file(GUCC_TEST_DIR "/files/locale.gen", dest_locale_gen, fs::copy_options::overwrite_existing);
+
+    // set test locale.
+    assert(gucc::locale::prepare_locale_set("ru_RU.UTF-8"sv, folder_testpath));
+
+    auto locale_conf_content = gucc::file_utils::read_whole_file(dest_locale_conf);
+    assert(locale_conf_content == LOCALE_CONF_TEST);
+
+    auto locale_gen_content = filtered_res(gucc::file_utils::read_whole_file(dest_locale_gen));
+    assert(locale_gen_content == LOCALE_GEN_TEST);
+
+    // Cleanup.
+    fs::remove_all(folder_testpath);
+
+    assert(!gucc::locale::prepare_locale_set("ru_RU.UTF-8"sv, folder_testpath));
+}