Steve,
There are two languages we're talking about here, is that right?
As Aardvark says, in this area there are some 'low german' dialects. (note, despite what many people believe 'low' german and 'high' german (or 'platt deutsch' und 'hoch deutsch') don't refer to prestige, but simply the fact that high german is spoken in areas at a higher altitude, and low german dialects are primarily in the 'low countries' and environs). But that would probably be the german dialect you refer to.
The other language, ending in 'la'....I'm not sure. Here is a useful page on languages of Poland (as Silesia is now part of Poland):
http://www.ethnologue.com/show_country.asp?name=Poland
The languages which seem like possible candidates are:
'Belarusan' (a Slavic language - 'White Russian')
'Kashubian' (another Slavic language)
'Lower Silesian' (a dialect of German)
'Ukrainian' (another Slavic language)
unless you have Gypsy ancestors? This site also lists a number of 'Romani' dialects, but those are spoken by the Gypsies. (Interestingly though, the Gypsies are originally from India, and so the Romani dialects are closely related to languages like Hindi and Nepali).
a few more sites of interest:
http://216.239.41.104/search?q=cach...wiki/Silesia+Silesia+languages&hl=en&ie=UTF-8
http://www.polishroots.org/genpoland/sil.htm
this may not be that helpful as yet. let me know if any of the language names sound right to you. I'll keep thinking about it.
cheers
--B.