Hide lang switch separator if only a single lang is used

[wrobelda]

What does this PR change? What problem does it solve?

A language switch separator is displayed even if a website has a single language only. This fixes it by checking for AllTranslations size before adding the <ul class="lang-switch"> element.

Before:

After:

Note that I have absolutely no experience with Golang, hopefully the is up to the standards.

PR Checklist

• [x] I have enabled maintainer edits for this PR.
• [x] I have verified that the code works as described/as intended.
• [x] This change does not include any CDN resources/links.
• [x] This change does not include any unrelated scripts such as bash and python scripts.