EPiServer UI is using localization service under the hood. You can specify the language in the language node, as follows:
<language name="English" id="en">
The display attribute supports only one language (Name and Description values), so it's recommended to localize strings in the XML file(s) instead.
You can set up Alloy sample project, and take a look at XML files in Resources/LanguageFiles folder.
or use database driven localization provider instead of xml one ;)
1) Localizing content language(for web site visitors) and localizing editor UI language (for content editors). Are these two implemented differently in Episerver?
There are two ways to localize.
What I do not understand is how to get the localized string when there are multiple languages mentioned here?
2.2) Localization service API
This is clear. But can this be used in localizing editor UI language (for content editors)?
The example for #2.1