Make dates respect current locale (deprecations!)

And make comments use it in a smart way (it's not but it works)

Deprecate "extra.date_format" and "extra.comments.locale" and replace it
with "date_format" and "date_locale" in translation files

i18n/ru.toml

@@ -1,5 +1,11 @@
-language_name = "Русский"  # Shown in language picker for multi-language sites.
-date_locale = "ru-RU"
+# Shown in language picker for multi-language sites
+language_name = "Русский"
+# Tera date format used for listing posts
+# (post publication date, tag posts list...).
+# Not used in comments, "date_locale" is used instead.
+# See https://docs.rs/chrono/0.4.31/chrono/format/strftime/index.html
+date_format = "%d %B %Y г."
+date_locale = "ru_RU"
 
 # Note on pluralization prefixes:
 # - few_: for numbers ending in 2-4, except 12-14, in genitive singular.