Talk:Improving English language strings
From MoodleDocs
Changing or creating a new lang string?
New strings were required in 1.x times when we did not have branches for translations. Since 2.0, for changes in master, structural and/or semantic modification of a string (such as adding or removing {$a} placeholders etc) is acceptable as such strings are highlighted in AMOS as outdated. Of course, if lang pack maintainers do not pay attention to it, mismatch can happen - but is is considered to be the lang pack bug.
When a new string is introduced, the old one should be deprecated or removed so that unused strings do not accumulate.