So I may be speaking out of turn... being over here in the States renders my input questionable, I'll admit. Also, my one visit to Wales was a cycling trip from Holyhead to Cardiff back in 2009. So I may be ignorant of a fair bit of nuance.
But as an American it's my civic duty to give an opinion whether its wanted or not [really, it's in our Constitution, I think].
Anyway, I grew up just south of Quebec in the 80's. Montreal was where I went for concerts and cultural events through all of my adolescence. At that time there was a great deal of concern and strife about preserving the French language and culture. Advertising was mostly in English, most announcements were made in English first, and studies showed a decreasing usage for French in day to day life. It was a stressful time for the province because many felt that French culture was dying.
Over the summer, I visited Montreal for the first time in 20-some years and found a complete change. All ads and most signs were in French only, announcements were primarily given in French, and I heard the language being spoken everywhere. Even little things like being greeted by the waitstaff in French had me trying to cast my mind back to the few (polite) phrases I could remember.
From what our hosts said, the change really started with The Charter of the French Language, which might be worth a look for ideas that could be adapted to Wales.
I realize it's different since Quebec was/is majority French-speaking, however there are some things that might be applicable. I'm thinking specifically of the fundamental language rights. Also, our hosts said that new immigrants to Quebec (whether coming from other parts of Canada or outside the country) has to learn French as part of the immigration process.
So that's what I've got, for what it's worth.