PBCKP-97: Adding localization files

	Added localization of messages. Fixed some bugs.
	Added the --enable-nls tag for tests.
	Added a test to check the localization of messages.

Author: MakSl

README.md

@@ -224,3 +224,17 @@ Postgres Professional, Moscow, Russia.
 ## Credits
 
 `pg_probackup` utility is based on `pg_arman`, that was originally written by NTT and then developed and maintained by Michael Paquier.
+
+
+### Localization files (*.po)
+
+Description of how to add new translation languages.
+1. Add a flag --enable-nls in configure.
+2. Build postgres.
+3. Adding to nls.mk in folder pg_probackup required files in GETTEXT_FILES.
+4. In folder pg_probackup do 'make update-po'.
+5. As a result, the progname.pot file will be created. Copy the content and add it to the file with the desired language.
+6. Adding to nls.mk in folder pg_probackup required language in AVAIL_LANGUAGES.
+
+For more information, follow the link below:
+https://postgrespro.ru/docs/postgresql/12/nls-translator

nls.mk

@@ -0,0 +1,6 @@
+# contrib/pg_probackup/nls.mk
+CATALOG_NAME     = pg_probackup
+AVAIL_LANGUAGES  = ru
+GETTEXT_FILES    = src/help.c
+GETTEXT_TRIGGERS = $(FRONTEND_COMMON_GETTEXT_TRIGGERS)
+GETTEXT_FLAGS    = $(FRONTEND_COMMON_GETTEXT_FLAGS)