Throw an error dialog when an installation of language failed

[ryonakano]

Prerequisites

• [x] I have searched open and closed issues for duplicates.

Describe the bug

If an installation of language failed, no error dialog is shown thus there's no way for users to know if the installation succeeded or failed.

To Reproduce

~1. Turn off your Internet connection so that fetching the language pack gets impossible and the installation fails

2. Open the Locale Plug and try to install some language
3. The installation dialog is shown but soon disappeared
4. The language list in the left pane is updated but the language you chose is not there because its installation failed. Nevertheless, no error dialog is shown~

Edit: the above method seems to be invalid… :thinking: I don't know how to trigger an error but as far as seeing the source code all try {…} catch {…} sentences only have a warning and don't seem to show anything to the UI.

Expected behavior

An error dialog is shown if an installation of language failed.

Platform Information

• [x] I'm using the latest version from git that I've manually compiled
• [ ] I'm using the latest released stable version

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