[UX] Leave language dropdown menu in the top nav, use icon for title

[chalin]

Both the language menu and the search box in the top nav move to the side nav when the display gets narrow. This has been a source of confusion for many users and site designers. I'd like to suggest the following (IMHO) improved design for the language menu

• Leave the language menu in the top nav for all display widths
• Consider the option of having a shorter menu title, such as a globe:

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Other thoughts about the menu title:

• By default, we'd show only the icon, which could be set via CSS, via :after for easier customization. And the current language could be hidden by default (again via CSS).
• An alternative icon could be the language icon, but visually it is difficult to make out, even if set to a larger font size:

@svrnm @theletterf, this is proposed as a solution to:

• Language Selection is not visible in mobile view open-telemetry/opentelemetry.io#4597