can't install another language keyboard

[kris84]

I just upgraded to the new 4.6 release hoping to resolve an issue I'm having. I've been trying to install a second language keyboard to the system, but when I go to Language Support, here's what happens. When I open it I get this message:

The language support is not installed completely.
thunderbird-locale-en-gb
firefox-locale-en
thunderbird-locale-en
thunderbird-locale-en-us

So I tell it to try to install but get this:

Could not install the full language support. Transaction failed: Package dependencies cannot be resolved. The following packages have unmet dependencies:
thunderbird-locale-en: Depends: thunderbird (>= 1:60.8.0+build1-0ubuntu0.18.04.1) but 1:60.8.0+build1-0ubuntu0.18.04.1 is to be installed

So, okay, back in the Language Support dialog box, I click Install/Remove languages, select Russian and proceed. But I get an error message that says "Software database is broken. It is impossible to install or remove any software. Please use the package manager "Synaptic" or run "sudo apt-get install -f" in a terminal to fix this issue first."

Running that in a terminal gives:
Reading package lists... Done
Building dependency tree     
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

Can someone tell me what I'm missing?