What happens if I don't pay a speeding ticket and am a foreigner? I recently found out, since it is not my native language, that it wasn't just a warning - it was actually a ticket.
The exact situation depends on where you are. If you are in Washington state, what you get (but did not realize) is a notice to appear in court. By not paying the fine or showing up to court, you could be subject to RCW 46.64.025, so that the department of licensing is notified. You have 15 days to respond to the notice. We assume that you are a resident, because if you are a non-resident (and not resident of another state with a reciprocal agreement), they would have required you to pay a bond at the time of the ticket (though that isn't possible with automated infraction-detection).
When the Dept. of Licensing gets the notice of the unpaid ticket, they may suspend or revoke your license. At this point, you will have received notice that your license was suspended (unless you changed your address and mail isn't forwarded, in which case you have a different problem, that you're supposed to apprise DOL of your current address, and didn't do so). At that point (after they send the letter), you have 15 days to respond. One response is to pay the ticket plus the added fines, or, you can request an administrative review (to appeal the suspension).
The point of going to court to plead your case would presumably be to modify the judgment against you, for instance to reduce or eliminate the added fine. You would then need to give a good reason for not being punished: RCW 46.64.025 already has you covered, because the suspension process starts with willfully failing to appear. You would then need to show that your failure to appear was not willful.
It does not legally matter whether you are a foreigner or have problems understanding the language. Speeding tickets usually say pretty clearly that you must pay the ticket within a specified time frame, or appear in court, but people don't always read tickets. It is entirely plausible that one's grasp of the language is low enough that there really was a misunderstanding. If you can provide credible evidence that your failure was not willful, by law you would only be liable for the ticket.
In other states and countries, the situation could be somewhat or quite different (e.g. Norwegian traffic laws are stricter). In New Mexico, it is more serious to fail to appear. NM Statute 66-8-126 states that "It is a misdemeanor for any person to violate his written promise to appear in court, given to an officer upon issuance of a uniform traffic citation, regardless of the disposition of the charge for which the citation was issued". Your license can/will be suspended (it is not clear whether suspension is automatic), but additionally since failure to appear is a misdemeanor, you can be arrested. Unlike Washington law, there is no willfullness requirement for such a penalty. Given the criminal nature of failure to appear, a traffic attorney would need to suggest an appropriate belated response.