Last night at the Polyglot conversation group a friend who is learning Welsh told me about the difficulties he had when trying to buy a train ticket to Dolwyddelan, a small village in the Conwy valley in North Wales. None of the ways he tried to pronounce it were understood by the ticket seller, so he ended up spelling it out. I also wasn’t sure what place he was referring to until he spelled it for me, even though I’m used to hearing mispronounced versions of Welsh place names.
In Welsh word stress almost always falls on the penultimate (last but one) syllable, so in Dolwyddelan it’s on the ddel, i.e. /dɔlʊiˈðɛlan/. If you put the stress anywhere else words just sound wrong or incomprehensible.
In languages like Welsh where there stress is usually in the same place it’s not so hard to get it right, but in languages with irregular stress placement, like English and Russian, it’s more difficult. You can try to learn where it goes in each individual word, and/or try to develop an instinct for it through extensive listening. I think I’m beginning to do his for Russian.