A state-of-the-art approach for generating such text is based on an expert annotator whose job is to decide which words to "switch out" with novel foreign words (from hereon we will refer to the "switched out" word as the source word and to the "switched in" word as the target word).
the process is labor-intensive and leads to a "one size fits all solution" that is insensitive to the learner's skill level or vocabulary proficiency.