Note that while monetizing itself is legal, the project that is based on a GPL software must (obviously) comply with GPL:
Any browser-side source code (which is distributed to users) has to be released under the same license
All copyright notices (e.g.
Copyright (c) 2019 Hunter Parcells) in such files must be preserved, with additional copyright notices in files that have been modified.
If the original game had an interactive notice with copyright/attribution statement (e.g. "About" page), that notice should also be preserved / amended as necessary.
Any additional terms from section 7 must be observed.
AdSense itself is not a problem. Many CMS are released under GPL (e.g. Drupal), and those are compatible with AdSense.
If your game runs mostly (or entirely) server-side, you're out of luck. There's no requirement for the new authors to release the code (and thus GPL terms do not apply), and if you were to copy their translated text and release a Spanish version of the original game, you'd violate their copyright. Unless, of course, the forked repository is public, so that its content can be considered to be released.
What open-source games often do to keep spin-offs under control is having a separate license for artwork. If that is the case, you can claim copyright violation for images / sounds, if the project in question reuses those.