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/jdautoenc.lang

@@ -1,22 +1,22 @@
-001 jdautoenc has already been started, wait for it to finish.
-002 Delete
-003 source file
-004 Error deleting source file
-005 Duration of the video does not match!
-006 Could
-007 not with
-008 convert
-009 Start
-010 script
-011 is a
-012 anime
-013 Checking video codec.
-014 Encode from
-015 to
-016 is already HEVC, check audio codec. If in eac3 or dts then encode audio to AC3.
-017 move
-018 to rename.
-019 Series
-020 remove jdautoenc.lock
-021 empty folder in unpack directory.
-022 Movie
+already_started jdautoenc has already been started, wait for it to finish.
+delete Delete
+source_file source file
+error_deleting_source Error deleting source file
+duration_mismatch Duration of the video does not match!
+could Could
+not_with not with
+convert convert
+start Start
+script script
+is_a is a
+anime anime
+checking_video_codec Checking video codec.
+encode_from Encode from
+to to
+already_hevc is already HEVC, check audio codec. If in eac3 or dts then encode audio to AC3.
+move move
+to_rename to rename.
+series Series
+remove_lock remove jdautoenc.lock
+empty_folder empty folder in unpack directory.
+movie Movie