Hello Kris ,
welcome to IMSLP and thanks a lot for your translation! The Thai version Main Page in Thai is now available on the main pages as "ภาษาไทย". (I've copied this from Wikipedia. Is it correct?) Regarding page titles: if the English version has a "IMSLP:***" or "Help:***", please use also this namespace. The "rest" of the title you can translate into Thai, like it's done here for example in Japanese IMSLP:参加者便利帳. If you want to continue I recommend to translate step by step the other pages which are linked from the main page (e.g. the Contributor Portal, Public Domain).
There's now a new category Category:Translations th which shows all the new pages. You can categorize them by adding the Template
{{AutoOldtrans
|Base Page=<here give the name of the English base page>
|Base Revision=<version id of the page>
|Language Code=th
}}
on each of your new pages.
Concerning your question how to translate the remaining English text on the main page: the words/headings "Featured:", "New Scores:", "New Recordings:", "News" are somewhat hidden, but are plain text in the code, so you can easily translate them. The links in "Featured" you can find in IMSLP:Featured/Links, which uses a kind of inline translation with the #iflang. For each |en= you can add a |th=<Thai translation>. Similar for "News": here the templates (1, 2, 3, 4) are used, also with #iflang. For the content itself it's not necessary to translate it because these are mostly just links to work pages and therefore should be understandable. If you have any questions you can ask me, of course. Thanks and Regards, Hobbypianist 17:33, 2 January 2012 (UTC)
