"Wales won the game."
Translation:Mi enillodd Cymru'r gêm.
Do you mean in order to emphasise Cymru? Very simple in this particular case - you simply change the order of the words, remembering that you need to keep the verb in the past (not change it to the present tense, as you have in your example):
- Cymru (a) enillodd y gêm, dim Ffrainc. - Wales won the game, not France.
The a there is optional in the colloquial language, and not something that is covered on introductory courses such as this one. (It is not the same a as the one meaning 'and' - it is a relative pronoun meaning 'that/which/who/whom'.)