In those detailed tutorials, please follow a few steps to create a multilingual Joomla site.

• If you have Joomla 4.x or Joomla 5.x read: https://www.joomshaper.com/blog/how-to-create-a-multilingual-site-in-joomla-4-using-helix-ultimate
• If you still have Joomla 3.10 read: https://www.joomshaper.com/blog/how-to-create-a-multilingual-joomla-site-using-helix-ultimate

Good to know

• Joomla has a built-in tool named "Multilingual Status" (button at the top bar) that allows you to check what is wrong with current multilingual settings, and what is missing.
• Translating your Joomla site into different languages gives you a chance to start ranking in Google for queries in new languages.
• A multilingual website serves the same content in multiple languages. The webmaster has full control over what content will be translated. 
• Most extensions are translation-ready. However, they may not have translations for all languages, or some phrases are hard-coded.
• Try to avoid using Automatic translators especially if your site is for B2B, because linguistic and syntax errors can dramatically reduce the trust of business partners.

Useful video guides

• https://www.youtube.com/watch?v=nKR0OL2fOmg
• https://youtu.be/Opkj3X8vlO8?feature=shared&t=3681
• https://www.youtube.com/watch?v=9Dn_bakyACI

The most important tips

• Before you start, install the needed languages in Joomla and prepare professional translations.
• All articles, k2 items, modules, and Pages (SPPB) can be assigned to different, selected languages.
• If you have a Multilingual Site, an off-canvas (mobile) menu should also be prepared for each language.
• About Mobile Menu - remember to assign Menu modules in "offcanvas" position for each language.
• Don't use fonts that aren’t international, It’s an easy one to forget, but make sure you choose a font that displays special characters. French accents (like this: é) can change the meaning and pronunciation of a word, so they’re important to include and get right!
• It would be a good idea first to test your skills on a test site (subdomain) and verify that everything works correctly before you start making changes on the production website.
• And once you’ve translated your site, you can add and display a language switcher module.