Sets the list of directories where the this looks for language files.
If dirs is null, the search path is reset to default.
At the moment this function can be called only before the language files are loaded for the first time. In practice to set a custom search path for a `GtkSourceLanguageManager`, you have to call this function right after creating it.
Since GtkSourceView 5.4 this function will allow you to provide paths in the form of "resource:///" URIs to embedded `GResource`s. They must contain the path of a directory within the `GResource`.
| this | |
| dirs |
a null-terminated array of strings or null. |