Hi,
There is the language to be passed to the store( ) method as well - if you don't pass it, it seems to be saved in sy-langu... I was able to create Texts in EN and DE when I took over new_master_language to header-masterlang and then passed it on to store( ). I changed my previous post to reflect the code changes.
The languages other than masterlang are probably easiest created using translation functionality in Function group STXBT, namely SSFTR_SET_TEXT. There the guys have "cut the OO crap" and done it directly in stxftxt table... That FM, however, does not let to set the caption...
There probably are good reasons why SAP programmed this stuff the way they did, and I may expect "gratification" too soon when starting to work with code I don't know well... but the more I look at it the more I find SSF code irritating 
Couple of years ago I was trying to understand if there is easy way to program some kind of search for smartform. Then I pretty soon decided that it's not worth the time investment and started downloading to xml for searching...
cheers
Janis