1) Global Settings language depends on the browser language settings.
2) Course Catalog language is selected during Course Catalog creation process.
Please be aware: The Course Catalog site is created with all Alternate Languages selected, that's why Course Catalog Admin Center is displayed depending on the browser language. To avoid such a situation, navigate to the desired course home page > Site contents > Site Settings > Language Settings > click Show advanced settings and unselect all alternate languages in site collection’s Site Settings.
When you change the language for the already existing Course Catalog, some time is required for the changes to be applied. To speed up this process, you can clear Storage Cookies (or clear the whole Storage).
3) Course/TP Home Page inherits Course Catalog default language and alternate languages. Please visit this link to find more about what determines the language of the LMS365
Alternate languages can be checked in the Site Settings:
Subsite language is selected during its creation process from Settings > Site contents > New > Subsites.
Certificate language depends only on the Course Regional Settings (Site Settings→Regional Settings→Region→Locale). If you need to change the language or date format in the Course Certificate, this is done from the SharePoint local settings.
Notifications language is the Locale language specified on the Course level. To receive the notifications in the needed language, first select the locale of the Course Catalog, and then create a Course. If you change the locale of the Course Catalog you will still receive the notifications for the Course in the previously specified language.
Locale can be checked in the Site contents→Site settings→Regional settings→ Region→Locale.
7) Learning modules and quizzes language settings are covered by the Rules of LMS365 display language