In fact I'm not sure that this is a problem:
* it's possible that the (rare) Greek users are difficult to locate, and even in this case, that they currently don't use Greek as their prefered locale (they may use Limewire using the english interface: as there's no Greek translation available for now this will explain that fact; the only way to improve the situation for Greek users is to help LimeWire providing a Greek translation, because LimeWire has nobody knowing that language)
* do you see connections from Greek users (look at their domain name, you may see Greek ISP's) in the connection panes? if so, the preferencing does work; but connection preferencing only works if the Greek locale is selected in the limeWire interface, so there must be one. Otherwise the rare greek users are "lost" within an ocean of English-speaking users that share mostly English-written files.
* Even if Greek users are present, it's also possible that they don't share enough Greek files, but share more common files whose title is written in the Latin alphabet

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Right now I'm using LW 4.13.6 beta and it has a greek translation. Every version had one.

The weird thing is that I had be using for 2 years LW 4.8 - 4.9 and I had no problem searching in greek even when using the english interface.

You 've right though that no connection are made from/to greek ISP's