Generally, plea bargains also include a stipulation that you're waiving your right to appeal, however, if you truly did not understand and the plea is involuntary (particularly if you did not have or were not offered a translator), you may have an outside chance. That said, Deferred Adjudication isn't a right, it's merely an offer by the State that you can reject and Pre-Trial Diversion is never a guarantee (it's also at the State's discretion), so it's uncertain whether you would have qualified. Further, if you truly received Deferred Adjudication, then you should have the option for a Motion for Non Disclosure of your record (which should show that your case has been dismissed). You need to determine if your case has been dismissed (through Deferred Adjudication) or if you were convicted (with a probated sentence). Talk to a lawyer in your area who is familiar with these procedures and who has appellate experience.
You may be able to attack the conviction via a post conviction writ based on your plea being involuntarily made. You should contact a lawyer who handles those types of cases.
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You might be able to file a writ of habeas corpus either alleging that the plea was entered into involuntarily, or perhaps you could make an argument that you received ineffective assistance of counsel. Of course, the other issue is whether or not you still have a remedy after your term of deferred adjudication has ended and your liberty isn't restrained by probation any longer. I think it might be a longshot, but I think it might at least be worth looking into.