Please read http://docs.moodle.org/en/Translation
If it is not clear enough, please point out what, so the documentation can be improved.
To go short: since a few weeks, we don't use 1.5 anymore for the creation of translations. So we don't make any language packs but unicode language packs. Moodle 1.6 is especially tuned to do that , so please use 1.6 for your translations. A language pack for 1.6 could probably be used on a 1.5 if you copy the content of langconfig.php into moodle.php, but I wouldn't recommend doing that on production environment as a normal procedure
.My advise to you is:
- leave the current Greek installations as they are. The language pack hasn't been updated for more then 2 years, so it can wait another 2 months.
- for translationwork: do a download of an as recent as possible 1.6 (and update it regularly - eg weekly). Download the Greek utf8 translation and use that as a start. Please use the build-in editor for strings and helpfiles to avoid problems in your language pack.
- If you have already new files, follow the procedure above, replace the existing files in the el_utf8 language pack with your new files, open - check and save them with the Moodle build-in editor.