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 (Installed Languages list does not refresh on 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:

[ryonakano]

Works confirmed with installation/removal of Central Kurdish (ckb) and Japanese (ja), no regressions found. Thank you very much!