Always backup. Always share your mods with the community. And never forget: behind every dramatic 90th-minute winner or boardroom sacking you read in FM05, there was a line of code waiting in the English.ltf.
Re-download the vanilla file. Many FM community archives (FMBase, Sortitoutsi) still host clean backups of the v5.0.5 English.ltf file. Football Manager 2005 English.ltf
After editing, save the file. The editor must output the file as UTF-16 Little Endian (not ANSI or UTF-8). If you save incorrectly, FM05 will crash on launch. Always backup