We investigated reading and writing in two domestic languages (Swedish and Finnish) and one foreign language (English) among multilingual university students with (n = 20) versus without dyslexia (n = 20). Our analyses encompassed overall speed and accuracy measures and an in-depth analysis of grapheme-phoneme-grapheme errors and inflectional errors. Dyslexic impairments were most conspicuous in word and sentence segmentation, accuracy in oral text reading, single word writing to dictation and free writing across the three languages, most prominently in English. The writing tasks exhibited significantly higher proportions of phoneme-to-grapheme errors in the dyslexia group, especially in English, and marginal differences in inflectional errors, again discernible in English. The results indicate that language proficiency and orthographic depth modulate the appearance of high-performing multilinguals' dyslexic problems in reading and writing. These problems surfaced most clearly in a less proficient foreign, orthographically opaque language.