Having got a Samsung Galaxy Chat (B5330) I'd like to use its physical keyboard to to enter not only english but also central european (czech) and cyrillic (russian) letters (I am ok with english-only key labels). So, any directions on where and how?
You can try External Keyboard Helper, which is designed for bluetooth/usb keyboards but I believe it should work for the Chat's physical keyboard!
I had a similar issue as I was learning Spanish. I was finding it almost impossible to key in the Spanish words using English text, one by one character. To get round this, I enabled two languages and therefore my phone now recognises both Spanish and English words and therefore I have no problems when switching from contacting colleagues to learning languages. To do this, go onto 'Settings', then 'Language and input'. Then scroll down to the option titled 'Samsung keyboard' and click the setting cog next to it. You should then see an option called 'Input languages' and from there, you should see a list of all the available languages on your phone. Simply check all the tickboxes of any languages you would like to use and then those languages will be enabled and you'll be able to type with them throughout any app on your phone. Hope this helps and answers your question.
The problem is (at least was in the older and many newer versions of Android) there's not a simple way (to my knowledge - without adb/root) to add language layouts. Even the common ones like Czech (QWERTZ) were missing for a long time.
For a simple solution you want to find packaged keyboard layouts (usually tiny .apk) but be wary of malicious ones. If you want to create/import layout(s) I believe you should start looking into Key Layout Files (.kl) but I personally haven't done it that way.
For me, Raidsix Input Devices (.apk (<100kB)) helped back in the day (from Google Play, when it was there year(s) ago). However it isn't available anymore and there seems to be no official or trustworthy way to obtain it.
I still have it on my tablet so I shared it now with other tools to come in the future. Link [Mediafire]
You can try a 3rd-party keyboard like GO SMS Pro. It will allow you to use different keyboard layouts, including Russian. I think it has Czech (but probably not written in English).
You need to go into input properties and choose the languages you want.
If you do not find the desired language then you must root your phone and use an app like language enabler from Google Play.