Multi-Language: Second language ignored

Google indexes only pages from one out of the two languages in the website

[jb0217]

I have a 7 month old greek (.gr) website operating in both Greek and English. The greek pages are in a subdirectory www.domain.gr/main/, while the English pages are in www.domain.gr/en/. The url www.domain.gr points to www.domain.gr/main/index.htm. All the greek pages have links to the English version and vice versa. I also have an english www.domain.com redirecting (302) to www.domain.gr/en/index.html

My problem is that while more than 900 greek pages are indexed by Google, today my last Enlgish page (the home page) was removed from the index. Most of my pages in both languages have PR3 or 2, while the English home page has a PR4.

The English pages used to be indexed normally during the past months, and they first started disappearing during the last big index update in late April, when my site dropped down to 100 indexed pages, before coming back up to 900, but without any English pages among them.

I'm considering two probable causes for that: I keep the same file names for pages in both languages, though they are in different directories (eg. www.domain.gr/main/something.htm and www.domain.gr/en/something.htm)-changing that would be rather inconvenient for several reasons.
The other is that I don't have Content-Language meta tags (yet), which I intend to add.
Do you have any other ideas or suggestions?
Thanks in advance

[vincevincevince]

Two theories:-

1/ That you are in greece, and they are out of your index, but if I were to search from the UK then I'd see the english but not the greek pages (?)

2/ That google's cottoned on to the fact that the pages are duplicate content with only a chance in language (?)

[jb0217]

Both google.co.uk and google.gr today have my english home page back in their index today, but no other page is appearing. Yesterday, neither one had it. So I guess that's the way it's gonna go from now on, unless I do something. 2 months ago I used to have at least 100-150 though.
My main question is:does google use the page name to assess that a page is a duplicate even if the rest of the url is different? Is this pattern: www.domain.gr/main/page1.htm - www.domain.gr/en/page1.htm
considered duplication even if the pages obviously have different content? (since they are not even in the same language).
I would really like to avoid changing the names (for PR and other reasons), so is there another way out?
Also could it be a temporary after-effect of the update that will fix itself soon?(optimistic approach) Since my greek dropped pages came back in, can I hope the same for the English ones?