Developmental dyslexia is characterized by reading and writing deficits that persist into adulthood. However, the mechanisms underlying these deficits appear to affect several language domains negatively. The present study aims to investigate how 18 native Spanish-speaking adults with developmental dyslexia perform different language tasks in English as a foreign language. For this purpose, reading and oral comprehension were performed along with written and oral production tasks by adults with dyslexia and their control peers. The results suggest that Spanish adults with dyslexia need more time to read English texts, and their reading comprehension is significantly worse than that of the control group. In written production, differences from the control group were found in the number of spelling errors. In addition, the oral productions showed differences in semantic errors, lexical diversity, and sentence complexity. Interestingly, the group differences for all measures were greater for the oral than for the written production tasks, leading to the hypothesis that this population is negatively affected by the spontaneity of the situation. In terms of practical implications, it seems important to provide special support for adults with dyslexia not only for written language learning but also for oral language learning in English.