Single Welsh translator button

I’ve been through various forums, lots of info but never finding the exact way of accomplishing what I need to create.

What I need is to have a single button in the header that users can flip between English and Welsh (Cymraeg).

I just tried a translator widget (Multilanguage by BestWebSoft) this has Welsh in it, it appears as a drop down menu which I’ve only been able to add in a page.

I’m using Tyler’s Tesseract theme so he does have buttons in the header which at the moment I’ve removed, would it be possible to convert one of these?

I’ll give you an example of a website which has such translation switch button situated at the top https://www.aberystwythartscentre.co.uk/
Don’t know if they use a translating machine or write two websites in both languages.

If anyone has done this or have ideas of the best way to approach it that would be a big help.