slavery is insinuating that they were forced into labor at gunpoint, not that they signed a contract to work for a company
indentured servitude is effectively slavery because there is no practical exit path, even if it was entered willfully in some way. you have no volition after the initial agreement is finalized. agreements such as these are inherently unfair regardless of the circumstances, and the employers are likely well aware that the employees are incapable of fully understanding the consequences of the agreement and are unable to afford a third party interpreter
the thing about a contract is that it is legally binding as well. if the worker has a contract that ties them to this role, they may face legally backed repercussions for failing to uphold their end. i don't think this can possibly be construed as a good thing, or one where it's simply the fault of the worker