Postby Vlürch » 2016-06-14, 11:58
I'm not fluent in any Slavic language, but I know at least some Finns have problems pronouncing [z] and [x]; [z] doesn't exist in Finnish and is replaced by [s], [t͡s] or [t͡ʃ] and [x] is replaced by [h] even though it can exist as an allophone, so basically it's treated as the same as [h] and the difference isn't noted. The contrast between [l] and [ɫ], along with palatalisation, is incomprehensible to most Finns if they aren't into linguistics. Sounds that exist in Polish that the average Finn isn't at all familiar with are nasal vowels, [ʂ], [t͡ʂ], [d͡ʐ] and [ɣ]; they're most logically replaced with [ʃ], [t͡ʃ] and probably [g] or [r] if interpreted as if it was a speech impediment. [ɕ] and [ɲ] would just be interpreted as [ʃ] and [nj], while [ʐ] and [ʑ] both become [ʒ~d͡ʒ] due to familiarity with English and loanwords even if it isn't generally pronounced that way.
So, in terms of transcription, something like this is probably the most comprehensible while still being somewhat accurate:
ś > š; sh if it's for kids*
dz > ts
dź > dž; j if it's for kids**
dż > dž; j if it's for kids**
ch > gh, h
ń > nj
sz > š; sh if it's for kids*
ć > tš; ch or tsh if it's for kids***
cz > tš; ch or tsh if it's for kids***
w > v****
ł > l
*sadly, the use of š is declining, but sh is technically wrong
**dž is only used in a few loanwords; j is pronounced [j], but it's a common substitution
***č is replaced with tš, so without š, using ch is assumed to be like in English
****Finnish doesn't have [v] or [w], only [ʋ]; it used to be written w but was changed to v