Expanding a website to a global audience: start from scratch or not?

Hello everyone,

I currently have a website whose main audience is Italy. For a lot of reasons I'd like to expand the website to a global audience (it's a gaming blog), writing content in English and doing the usual stuff.

Where is the problem? I have a lot of content (14K+ posts on WordPress!) written in Italian, and if I decide to change language for the website, will it cause problems in terms of SEO and Google Search? Because I honestly don't think that keeping a website with content in different languages and not translated is a good thing.

However, the other problem is that if I create a completely new website with a new domain, I'd basically lose everything I've done until now.

So, the question is: what should I do? Thanks in advance for your answers.