Как локализовать программу C++/cmake с помощью GNU gettext

как генерировать файлы .pot

Вы пишете их вручную или генерируете с помощью msginit. Это то же самое, что и .po, просто другое название документации.

Не могли бы вы привести пример использования GNU gettext для локализации следующей программы

Следующий:

cat >./CMakeLists.txt <<EOF
cmake_minimum_required(VERSION 3.11)
project(trans)
include(CTest)
add_executable(main main.cpp)
file(GLOB ffs "lang/*.po")
set(TEXTDOMAIN myprogram)
make_directory(${CMAKE_CURRENT_BINARY_DIR}/locale)
foreach(ff IN LISTS ffs)
  get_filename_component(lang ${ff} NAME_WE)
  make_directory(${CMAKE_CURRENT_BINARY_DIR}/locale/${lang})
  make_directory(${CMAKE_CURRENT_BINARY_DIR}/locale/${lang}/LC_MESSAGES)
  add_custom_command(
    OUTPUT
      ${CMAKE_CURRENT_BINARY_DIR}/locale/${lang}/LC_MESSAGES/${TEXTDOMAIN}.mo
    DEPENDS
      ${ff}
    COMMAND msgfmt -o
      ${CMAKE_CURRENT_BINARY_DIR}/locale/${lang}/LC_MESSAGES/${TEXTDOMAIN}.mo
      ${ff}
  )
  add_custom_target(gen_${lang} ALL DEPENDS
    ${CMAKE_CURRENT_BINARY_DIR}/locale/${lang}/LC_MESSAGES/${TEXTDOMAIN}.mo
  )
  add_test(NAME ${lang} COMMAND main)
  set_property(TEST ${lang} APPEND PROPERTY ENVIRONMENT
    TEXTDOMAINDIR=${CMAKE_CURRENT_BINARY_DIR}/locale
    LANGUAGE=${lang}
  )
  set_tests_properties(${lang} PROPERTIES
    PASS_REGULAR_EXPRESSION "${lang} foo"
  )
endforeach()
EOF

cat >./main.cpp <<EOF
#include <iostream>
#include <string>
#include <libintl.h>
#include <cstdlib>
#include <clocale>
int main() {
        setlocale(LC_ALL, "");
        const char *textdomainstr = "myprogram";
        const char *textdomaindir = getenv("TEXTDOMAINDIR");
        if (textdomaindir) {
                bindtextdomain(textdomainstr, textdomaindir);
        }
        textdomain(textdomainstr);
        //
        std::string name = "foo";
        std::cout << gettext(name.c_str()) << "\n";
}
EOF

cat >./lang/de_DE.po <<EOF
msgid ""
msgstr ""
"Project-Id-Version: PACKAGE VERSION\n"
"Last-Translator: Automatically generated\n"
"Language-Team: none\n"
"Language: de\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=3; plural=(n==1 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2);\n"

msgid "foo"
msgstr "de_DE foo"

EOF

cat >./lang/en_US.po <<EOF
msgid ""
msgstr ""
"Project-Id-Version: PACKAGE VERSION\n"
"Last-Translator: Automatically generated\n"
"Language-Team: none\n"
"Language: en\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=3; plural=(n==1 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2);\n"

msgid "foo"
msgstr "en_US foo"

EOF

cat >./lang/pl_PL.po <<EOF
msgid ""
msgstr ""
"Project-Id-Version: PACKAGE VERSION\n"
"Last-Translator: Automatically generated\n"
"Language-Team: none\n"
"Language: pl\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=3; plural=(n==1 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2);\n"

msgid "foo"
msgstr "pl_PL foo"

EOF

Результат:

+ cmake -H. -B./_build --no-warn-unused-cli -DCMAKE_VERBOSE_MAKEFILE=1 -DCMAKE_EXPORT_COMPILE_COMMANDS=1 -DCMAKE_C_FLAGS=-Wall -ggdb3 -Wno-unused-function -fsanitize=address -fsanitize=undefined -fsanitize=pointer-compare -fsanitize=pointer-subtract -DCMAKE_CXX_FLAGS=-Wall -ggdb3 -Wno-unused-function -fsanitize=address -fsanitize=undefined -fsanitize=pointer-compare -fsanitize=pointer-subtract -DCMAKE_RUNTIME_OUTPUT_DIRECTORY=bin -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=lib -DCMAKE_ARCHIVE_OUTPUT_DIRECTORY=lib -G Ninja
Not searching for unused variables given on the command line.
-- The C compiler identification is GNU 12.2.0
-- The CXX compiler identification is GNU 12.2.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /dev/shm/.1000.home.tmp.dir/_build
+ cmake --build ./_build --parallel --verbose
[1/5] cd /dev/shm/.1000.home.tmp.dir/_build && msgfmt -o /dev/shm/.1000.home.tmp.dir/_build/locale/de_DE/LC_MESSAGES/myprogram.mo /dev/shm/.1000.home.tmp.dir/lang/de_DE.po
[2/5] cd /dev/shm/.1000.home.tmp.dir/_build && msgfmt -o /dev/shm/.1000.home.tmp.dir/_build/locale/en_US/LC_MESSAGES/myprogram.mo /dev/shm/.1000.home.tmp.dir/lang/en_US.po
[3/5] cd /dev/shm/.1000.home.tmp.dir/_build && msgfmt -o /dev/shm/.1000.home.tmp.dir/_build/locale/pl_PL/LC_MESSAGES/myprogram.mo /dev/shm/.1000.home.tmp.dir/lang/pl_PL.po
[4/5] /usr/bin/c++   -Wall -ggdb3 -Wno-unused-function -fsanitize=address -fsanitize=undefined -fsanitize=pointer-compare -fsanitize=pointer-subtract -MD -MT CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d -o CMakeFiles/main.dir/main.cpp.o -c /dev/shm/.1000.home.tmp.dir/main.cpp
[5/5] : && /usr/bin/c++ -Wall -ggdb3 -Wno-unused-function -fsanitize=address -fsanitize=undefined -fsanitize=pointer-compare -fsanitize=pointer-subtract  CMakeFiles/main.dir/main.cpp.o -o bin/main   && :
+ cd ./_build && ctest -V 
UpdateCTestConfiguration  from :/dev/shm/.1000.home.tmp.dir/_build/DartConfiguration.tcl
Parse Config file:/dev/shm/.1000.home.tmp.dir/_build/DartConfiguration.tcl
UpdateCTestConfiguration  from :/dev/shm/.1000.home.tmp.dir/_build/DartConfiguration.tcl
Parse Config file:/dev/shm/.1000.home.tmp.dir/_build/DartConfiguration.tcl
Test project /dev/shm/.1000.home.tmp.dir/_build
Constructing a list of tests
Done constructing a list of tests
Updating test list for fixtures
Added 0 tests to meet fixture requirements
Checking test dependency graph...
Checking test dependency graph end
test 1
    Start 1: de_DE

1: Test command: /dev/shm/.1000.home.tmp.dir/_build/bin/main
1: Working Directory: /dev/shm/.1000.home.tmp.dir/_build
1: Environment variables: 
1:  TEXTDOMAINDIR=/dev/shm/.1000.home.tmp.dir/_build/locale
1:  LANGUAGE=de_DE
1: Test timeout computed to be: 1500
1: de_DE foo
1/3 Test #1: de_DE ............................   Passed    0.01 sec
test 2
    Start 2: en_US

2: Test command: /dev/shm/.1000.home.tmp.dir/_build/bin/main
2: Working Directory: /dev/shm/.1000.home.tmp.dir/_build
2: Environment variables: 
2:  TEXTDOMAINDIR=/dev/shm/.1000.home.tmp.dir/_build/locale
2:  LANGUAGE=en_US
2: Test timeout computed to be: 1500
2: en_US foo
2/3 Test #2: en_US ............................   Passed    0.01 sec
test 3
    Start 3: pl_PL

3: Test command: /dev/shm/.1000.home.tmp.dir/_build/bin/main
3: Working Directory: /dev/shm/.1000.home.tmp.dir/_build
3: Environment variables: 
3:  TEXTDOMAINDIR=/dev/shm/.1000.home.tmp.dir/_build/locale
3:  LANGUAGE=pl_PL
3: Test timeout computed to be: 1500
3: pl_PL foo
3/3 Test #3: pl_PL ............................   Passed    0.01 sec

100% tests passed, 0 tests failed out of 3

Total Test time (real) =   0.04 sec

как создать файлы .pot с заданной структурой проекта

Я всегда понимал, что .pot файлы — это .po файлы. Они одинаковые. Вы их пишете, или позволяете msginit сгенерировать их из файла шаблона, где этот файл шаблона также был написан вами, или сгенерирован каким-то скриптом. Я понял, что это намек в документации типа msgmerge, что это разные файлы, типа .pot имеет только один перевод и msgmerge обновляет его в .po файле.

Вы должны сгенерировать .mo файлы в правильной <lang>/LC_MESSAGES/<textdomain>.mo директории и структуре имен.