When and when not should I use the euphony rule?
I've never been to Ukraine, so I would like to ask some real Ukrainians this. When and when not should I use the euphony rule and also pronounce в like a /w/? I know when в is pronounced differently but should I do this in everyday speech? Personally, I prefer the sound of it but does it sound overly formal if pronounce things like piwden', wtrata, u mene ye instead of pivden', vtrata and v mene ye?
1) verb endings in past masculin -в : був /buw/, писав /pysaw/ etc are always pronounced /-w/
2) preposition в (=in) according to euphony rules in some cases in written must be changed to у, both в and у are often (not always) pronounced /w/ - all variants will be acceptable
3) for me pronouncing piwden', wtrata sounds exaggerated, pivden', vtrata more natural
4) funny that Latin diphtongs au, eu are pronounced with /v/, not /w/ in respective words; авто, евкаліпт... (though eu more often became ей)
But generally most people simply do not pay attention to these subtleties, like Spanyards to /b/ and /v/
There is no such thing as 'formal' pronouncing in Ukrainian. Even TV announcers on different channels follow different standards.
A bit formal is to pronounce plosive ґ when necessary (ґрунт, ґудзик etc), but also people pronounce it as fricative г, especially that in most cases these words are written with 'normal' г (грунт, гудзик). Also in Russian the 'shebboleth' for Ukrainians is fricative г.
So don't try to be hypercorrect. Simply say as it is written, and it will be OK in all circumstances