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_GB/removerename.lang

@@ -1,6 +1,6 @@
-001 Select the entry to be deleted:
-002 Exit
-003 Are you sure you want to
-004 delete
-005 want?
-006 Invalid entry.
+select_delete Select the entry to be deleted:
+exit Exit
+sure_delete Are you sure you want to
+delete delete
+want want?
+invalid Invalid entry.