Got this as Welsh-to-English. The tips say "Better to start with 'Sioned is...'" rather than "Alys's bride is...", and dinged me for the latter.
But it's been my experience that in simple "yw" statements, Welsh tends to put the "new information" first - where English tends to put it last. Look at many Welsh Wikipedia articles, and they start out with "(Long explanation) yw (article title)." For examples:
Ryan Davies: "Canwr a digrifwr Cymreig oedd Ryan Davies (22 Ionawr 1937 - 22 Ebrill 1977)" vs "Ryan Davies (22 January 1937 — 22 April 1977) was a versatile popular Welsh entertainer of the 1960s and 1970s."
Cardiff: "Prifddinas Cymru yw Caerdydd (Saesneg: Cardiff);" vs "Cardiff (Listeni/ˈkɑːrdɪf/; Welsh: Caerdydd (info) [kairˈdiːð, kaˑɨrˈdɨːð]) is the capital and largest city in Wales and the tenth largest city in the United Kingdom."
Calon Lân: "Emyn Cymraeg a ysgrifennwyd yn y 19eg ganrif gyda geiriau gan Daniel James (Gwyrosydd) a thôn gan John Hughes yw Calon Lân." vs "Calon Lân is a Welsh hymn, the words of which were written in the 1890s by Daniel James (Gwyrosydd) and sung to a tune by John Hughes."
Those were the first three Wales-related articles I thought to pull up.
Thus, when I encounter a simple "X yw Y" sentence, my instinct is to translate it as "Y is X", in that order.
Interesting! There is a similar construction in Irish when using the copula, 'is'.
Is X Y. Here X gives some information about Y.
It is rendered in English as 'Y is an X'.
Is feirmeoir é Seán is translated as 'John is a farmer' and not as 'A farmer is John'.
The general rule is to add 's to singular nouns and even though nouns ending with an 's' seem like an exception the following is from a highly respected source:-
"the Oxford English Dictionary states that while “practice varies, the best course is to add ‘s to names that end in –s when you pronounce the resulting form with an extra –s in speech (e.g. Charles’s, Dickens’s, Thomas’s, The Times’s); and omit the ‘s when the name is normally pronounced without the extra –s (e.g. Bridges’, Connors’, Mars’, Herodotus’)” (OED, 2005)."
Except that I've contradicted myself from 5 months ago, lol. OK, all variants of Alys's and Alys' to be added.