The language switcher widget offers language alternatives for each translated page. You can activate it like any other widget under Appearance/Widgets.
With Link text you can set the text that will be used for the links.
We recommend to use the option Text. This way, the language will be shown as it is written in that language: for German Deutsch, for Arabic العربية and for English English. This will help your visitors to find their language faster.
Flags are difficult: they represent countries, not languages, and some visitors might be offended when the see the wrong flag for their language. The Austrians for example are quite happy not to be a part of Germany.
The option Language code refers to ISO 639-1 codes: en for English, de for German and so on. Many readers don’t know what this is, so you should use that only if you have to save space.