Could it be toggles, like on our neighbours page?

It could (They actually redesigned the site 2 weeks ago!), but IMO since we only have two options it is unnecessary.

I think would be more accessible.

I don't know if there is a difference, maybe for screen readers? I tried to make it accessible by providing a label ("Sort languages by completion or name").

Could you move it to navbar, on the right?

Do you mean the current switcher, or the toggles? I think moving the switcher is fine, but the toggles may be troublesome on mobile, and also not particularly visible.

Could it be toggles, like on our neighbours page?

It could (They actually redesigned the site 2 weeks ago!), but IMO since we only have two options it is unnecessary.

IMO having two options is actually an argument for doing so, having too many of them would be an argument for a select box.

I think would be more accessible.

I don't know if there is a difference, maybe for screen readers? I tried to make it accessible by providing a label ("Sort languages by completion or name").

I mean more accessible even for me. I don't need to click the select box to see the options, if they are already there.

Could you move it to navbar, on the right?

Do you mean the current switcher, or the toggles? I think moving the switcher is fine, but the toggles may be troublesome on mobile, and also not particularly visible.

I mean toggles. I think we could break navbar into two lines on narrow viewports. I think on desktop it's just a good use of empty space, without shifting the main content lower.

PS we could generate static versions of dashboard per ordering, that would help with linking to a specific ordering, but it's just an idea, and a nitty-picky one.

Nice-to-have suggestion: option to sort by 30-day progress.