file mapper need to pass language in file_field_widget_uri data array

When importing translatables image fields which are using tokens in their field definitions, we need the file mapper to pass the current mapping language value to the $data array passed to file_field_widget_uri as third argument.
This way we let the opportunity to deal with the key used and translate it in another token name if needed.

Step to reproduce:

1. install a drupal with entity translation and at least 2 language (fr & en for example)
2. create a content-type with an image file marked translatable with a file directory value comporting a token: for example 'photos/[vd:language]'
3. create an importer with at least two mapping of that field (one mapping per language).

Expected result:

The media files should be placed in their respective language folder.

Actual Result:

When launching the importation process we don't have any information to get the correct file directory to save these images.