alert for browsers not using english language

Summary:
related to task: T1895
Browsers that do not return 'en-' from navigators.language check will see an error prompting them to add English to avoid translation errors.

Test Plan:
remove English from browser's list of languages
add any other language
npm start
navigate to settings tab
verify whether alert appears on page.

Reviewers: bytesofman, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: bytesofman, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10318