Sets language code for the Paragraph and optionally all runs under the paragraph.
SetLanguageCode(Language codes are formed as de-DE and is-IS for Iceland for example.
Note that Runs under the paragraphs do not always have same Language code as the paragraph it self. Which is why there is no setter for this property but instead there is a SetLanguageCode method.
Once a Paragraph has language code then the plugin will attempt to default new runs created on the paragraph to the set language code from the paragraph.