Disable the language selector in the account settings if only one locale is configured

Is your feature request related to a problem? Please describe.
Currently, when only one locale is configured on a Decidim platform, the language sector is still activated in the account settings, which is unnecessary as only one language can be selected (see attached screenshots).

Describe the solution you'd like
When only one locale is configured on Decidim, the language selector is disabled in the account settings.

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