mb_str_split() not supported in PHP 7.3

[Eruantron]

The library officially provides support for PHP 7.3 and later. However, I encountered an error when using PHP 7.3.

In deepl-php/src/GlossaryEntries.php, the function mb_str_split() is utilized, but it is only compatible with PHP 7.4 and newer versions.

[daniel-jones-deepl]

Hi @Eruantron, thanks for creating this issue, good catch. I'm surprised we didn't catch this earlier, because we test using PHP 7.3.

We have to look into how we could fix this, but it may be too much effort. Additionally, we are planning to drop support for PHP 7.3 beginning next year, because official support for PHP 7.3 ended almost two years ago.

[Eruantron]

Thanks for the feedback. I already thought it doesn't make sense to rewrite it for PHP 7.3. I've postponed the PHP migration for too long anyway, and now I have another reason for the revision.