German only is simple, as above. A greater difficulty is how to avoid the standard US version in favour of the UK version [the US guys want to force everybody to use their version].
I have a similar problem: residing in China, but speaking UK English. The main problem is the repositories: if the standard Ubuntu repositories are used, then only the US version can be installed. This means all emails are composed with USA spelling, not the desired UK spellings. [One would think a simple change in the config file is required to point to the language pack. But no, I could not find anything anywhere to customise TB to default to UK language and spelling.] My "solution" was to hack the install.
Before proceeding, readers should install "Synaptic" and be familiar with its menus and functions.
1/ get the latest release for the language you want.
1a/ Go to the Mozilla web page and download the language you want [UK in my case] from https://www.mozilla.org/en-US/thunderbird/all/
1b/ unpack the bz2 file to anywhere you want on your hardrive, example: \home\Tbird. [this results in many files and subdirectories]
2/ add the Mozilla ppa to Synaptic and update.
2b/ click Synaptic menu button "mark upgrades", then click "apply". Ths installs the latest TB release with all dependencies. [this ensures you get all the libs you need]
2c/ note: this results in a US version. the UK version is per step 3.
2d/ ensure TB is working after the above steps. [I had no troubles]
3/ find the installed TB files and overwrite them.
3a/ Ubuntu 16.10 installs the TB files in \usr\lib\thunderbird. [Ensure this applies to you]
3b/ copy all files/directories from \home\Tbird to \usr\lib\thunderbird and replace all files/directories.
3c/ you should have now the TB version you want [UK in my case].
4/ in Synaptic, uncheck the Mozilla ppa you added in step 1.
Why this works? Because TB is a stand-alone application package. Also, this hack enables anyone to install the very latest release [the repositories are often 2 releases out of date]. Hope this helps someone.