installer: Don't trim language codes

[davidmhewitt]

We cannot assume that language codes will be 2 characters long. This prevents the installation and removal of languages that have 3 letter codes and/or additional variants.

To test:

• With master, try installing the "Tatar, Crimean" (crh) language.
• Note that no progress indicator appears, and the language is not available after "installation". There is another bug that prevents the list updating after changes (#149), but even after a restart of the plug, "Tatar, Crimean" will not be available.
• Install this branch and try again.
• Note that the progress window does indeed appear this time
• After a restart of the plug, the language should be available.

[ryonakano]

Screenshot after installing and setting Central Kurdish as the system language with this branch: