Update localization-request.md to automatically add locale labels.

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Hey, as per our Slack thread here with @maudl-ext I wanted to have locale labels automatically added to new localization request issues.

The only way I could think of adding them automatically is having requestors delete the languages they don't need, which is a change in the way we were processing the requests. What do you think of this proposal? @rasamhossain @opysaryuk