Ideally you would help to finalize the greek translation, then you will never have problems later on. Because if you change this manual (which is possible) with each LS update there is a certain risk that the Greek language file you adapted is overwritten with the limesurvey standard one, which would be still lacking the translation.
this is all community driven, so it is free for everyone, but it can only survive it the users give back, either with donations of money, or with donations of their time and workforce. If you are not a developer, the translations are a good option to help.
I have seen that Greek is 94% complete, so there are missing 6%.
www.limesurvey.org/manual/Translating_LimeSurvey