Can you get the baseUrl for site by handle or id?
{% set site = craft.app.getSites().getSiteById(1) %}
{% set site = craft.app.getSites().getSiteByHandle('handle') %}
{{ site.baseUrl }}


But I would rather suggest you to grab the entries URL for a certain site in your language switcher

{% set entryInOtherSite = craft.entries.id(entry.id).siteId(2).one() %}
{{ entry.getUrl() }}


I'm not sure why you even ask this question since everything is well documented here since you "answered" that question