Is your feature request related to a problem? Please describe.

According to the official Google reference:
https://support.google.com/webmasters/answer/189077

Supported language/region codes

The value of the hreflang attribute identifies the language (in ISO 639-1 format) and optionally a region (in ISO 3166-1 Alpha 2 format) of an alternate URL. (The language need not be related to the region.) For example:

de: German language content, independent of region
en-GB: English language content, for GB users
de-ES: German language content, for users in Spain

Do not specify a country code by itself. Google does not automatically derive the language from the country code. You can specify a language code by itself if you want to simplify your labeling. Adding the country code after the language to restrict the page to a specific region. Examples:

be: Belarusian language, independent of region (not Belgium French)
nl-be: Dutch for Belgium
fr-be: French for Belgium 

Describe the solution you'd like

Allow saving language settings without specifying a country code.
Field: Language Tag

For example:
"en" or "de", without "en-GB" or "en-US"

Additional context

I do not want to limit the English language on my site to only one country - the United States or Great Britain. My site is not tied to a specific country; my site is tied to a language.

I believe that at the moment this is a very serious problem that must be resolved. It should be possible to save site settings without specifying a country.

This is still very bad for the SEO. For example, if I specify a country, then my site will be higher only in a certain country - for example, in the USA, because the country code is indicated, but in the UK the site will not have priority, despite the fact that the language on the site will be English.