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/rename.lang

@@ -1,19 +1,19 @@
-001 Wait for encoding to finish.
-002 Renaming is already running. Wait for it to run.
-003 Start
-004 Script
-005 Name
-006 does not match
-007 match.
-008 Go to next entry.
-009 Is a movie, extract names for folders.
-010 Create folder:
-011 Move 
-012 to
-013 Start renaming.
-014 If renaming successful,
-015 Delete
-016 folder
-017 Error during renaming!
-018 Failed attempts.
-019 Everything was completed successfully!
+wait_encoding Wait for encoding to finish.
+renaming_running Renaming is already running. Wait for it to run.
+start Start
+script Script
+name Name
+does_not_match does not match
+match match.
+next_entry Go to next entry.
+is_movie Is a movie, extract names for folders.
+create_folder Create folder:
+move Move
+to to
+start_renaming Start renaming.
+if_successful If renaming successful,
+delete Delete
+folder folder
+error_renaming Error during renaming!
+failed_attempts Failed attempts.
+completed_successfully Everything was completed successfully!