If ua-parser doesn't exist in your language, just pull the yaml file out of ua-core. That defines the regexes you should use and how they translate to browser versions (and os versions and devices).
https://developers.whatismybrowser.com/api/
As per modern web dev standards: you should always use feature detection not agent sniffing to handle cross browser issues; however having accurate user agent detection is really handy for trouble shooting customer issues, bot detection, spotting trends etc.
In reality, browsers have known bugs that last for years, you need to collect stats to figure out support policies, and you need to reproduce customer bugs.
Example: old versions of Firefox have an RCE vulnerability if you use third party jsonp apis. If you use these apis but don't block these ff versions, your users will be vulnerable.
We used ua-parser and everything went very smoothly.