I just downloaded an updated (bugfixed) extension that included a .i18n.php "shim" which said that it "maintains compatibility back to MediaWiki 1.17". However, versions prior to 1.20 only required php version 5.2.3, whereas it seems that the shim requires 5.3, which means that this shim does not necessarily provide compatibility back to MediaWiki 1.17. Surely this should be relatively easy to fix?
Topic on Talk:Requests for comment/Localisation format
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Yes, the issue is known. A patch is pending (and AFAIK ready) to fix it: gerrit:125706.
Running old core with latest extension is always risky. Many of the extensions already depend on PHP 5.3 regardless of the shims.