refactor: replace numeric translation keys with named keys

- Extract shared i18n.sh library with tr() function (replaces 5 duplicated text_lang functions)
- Replace numeric IDs (001, 002, ...) with human-readable keys (already_started, delete, etc.)
- Update all language files (en_US, en_GB, de_DE) to use named key format
- Update all scripts (jdautoenc, rename, addrename, removerename, config) to use tr() from i18n.sh

lang/en_US/addrename.lang

@@ -1,21 +1,21 @@
-001 Do you want a
-002 film
-003 or a
-004 anime
-005 series
-006 to rename? (Type exit to exit)
-007 Enter anime, series or movie
-008 By which
-009 keyword
-010 should the
-011 entry be matched?
-012 If you want
-013 now enter a second keyword
-014 This is the anime:
-015 Is this correct? (Y/n)
-016 Unfortunately your request could not be processed automatically. But you can still add an entry manually
-017 This is the series:
-018 This is the movie:
-019 Now enter the
-020 number.
-021 number in the URL
+add_prompt Do you want a
+film film
+or_a or a
+anime anime
+series series
+to_rename to rename? (Type exit to exit)
+enter_type Enter anime, series or movie
+by_which By which
+keyword keyword
+should_the should the
+entry_matched entry be matched?
+if_you_want If you want
+second_keyword now enter a second keyword
+this_is_anime This is the anime:
+is_correct Is this correct? (Y/n)
+manual_add Unfortunately your request could not be processed automatically. But you can still add an entry manually
+this_is_series This is the series:
+this_is_movie This is the movie:
+enter_now Now enter the
+number number.
+url_number number in the URL