The socio-economic importance of slate to Wales is pretty hard to avoid. You'll see it used everywhere, in various artworks, on the roofs of houses and inscribed in the quarried landscapes.
The Welsh economy of the 1800s was heavily dependent on the mining and processing of slate. It reached its heyday in the late 1800's when Welsh slate was being exported across the globe, to such distant climes as Australia and the Americas.
Quite a few of Wales' tourist attractions are now based in old quarries or mines, where you can go in and get an idea of what working life may have been like, the kind of conditions people worked and lived in. While slate is still processed on a much smaller scale nowadays, the version we see today as tourists is much sanitised, more gift shops and slate 'Cymru' coasters than the industrialised reality.
The hardships of such backbreaking work, the injuries and deaths that occurred in those conditions are hard to grasp. But also the sense of community that the mines engendered, where most workers were drawn from local Welsh speaking communities, does seem to remain in North Wales.
Slate continues to have socio-economic and cultural meaning for an understanding of Wales in both its past and present.
Welsh is also one of the most widely spoken of the Celtic language group, the first language of people as far apart as Argentina and New Zealand. As a child visiting Wales I was always aware of the Welsh language, but mainly through the odd sounding names of the towns and villages that we passed through. While I knew that most people understood some Welsh, and I even learnt a few words, I don't really recall hearing people speaking Welsh all that often.
While it is certainly the case that some people will only switch to Welsh when they hear an English accent, knowing that you won't understand their conversation, Welsh is definitely gaining ground as the vernacular in this part of the country. People's use of Welsh really depends on the social context of the conversation. Whatever the truth of my childhood memories, you will certainly hear people speaking Welsh in North Wales today, although absolutely everyone can also speak English.
The Welsh Language Act of 1993 has led to something of a resurgence and it's impossible not to see Welsh written all over the place. This can become confusing when road signs, shop signs, just about everything really, is bilingual - you can find yourself struggling to find the English signs in some shops which gets confusing.
You won't be expected to understand or speak Welsh, but some random words you might pick up are:
Croeso - Welcome
Cymru - Wales
Diolch - Thanks
Da boch! - Goodbye!
Stryd Fawr - High Street
Castell - Castle
Araf - Slow (seen on roads everywhere!)