I am reviewing a report as part of a university course, and the author of said report, a native Swedish speaker, has chosen to write the report in English rather than Swedish. Frequently, he uses grammatical structures from Swedish while writing English, and it ends up not making sense unless you translate it to Swedish word-by-word. Is there a term or name for this that I could use to describe what he is doing?
This is usually called interference. Here is the Wikipedia on the subject:
When the relevant unit or structure of both languages is the same, linguistic interference can result in correct language production called positive transfer: here, the "correct" meaning is in line with most native speakers' notions of acceptability. An example is the use of cognates. However, language interference is most often discussed as a source of errors known as negative transfer, which can occur when speakers and writers transfer items and structures that are not the same in both languages.
Usually this is done with native grammatical concepts mapped on secondary languages, in which case usually you'll see "L1 interference", with L1 meaning the first language one has learned.
Interference refers not only to grammatical concepts, but also vocabulary or other linguistic aspects. You'll also see this discussed with intrusion, when the first language "intrudes" into the second one.
Who knows, mаybe some of the Swedish grammatical structures he implants into English stick and become part of English grammar. A word, phrase or even a sentence imported that way into the language from other languages is termed a"calque". Of course, it is typically small languages that import calques from English rather than the other way around. Serbian speakers who rely on English in their daily communication in one or the other way are the main culprits for the development of calques in Serbian.
For Serbian speakers, there's a nice article on the subject here https://skolskiprogram.wordpress.com/2013/12/28/sintakticki-kalkovi-u-srpskom-jeziku-vec-od/ ). The author opens the article with an illustration for a calqued sentence : "Ne da ja znam, ali to sam samo ja." (from English : Not that I know, but that is just me.). This example brings another point to mind - calques are normally a matter of phraseology, collocation and semantics, rather than syntax. As the author says, the sentence "sounds Serbian" and I agree - it does sound Serbian enough and I'd say that it would easily pass as such in a more dynamic and elaborate conversation for example. The reason is that the syntax of it can readily pass as Serbian, but the semantics is alien to our language. Which brings up the question whether to refer to similar phrasings as "illiteracy", "calque", "an attempt at a calque", "not-as-yet-well established calque" or what else.
That said, I can remember quite a few newly-fangled phrases where the syntax is imported along with the meaning. One example that comes to mind immediately are nouns modifying other nouns. When you find such construction in Serbian, you found a calque.
Wikipedia has an interesting article on calques here https://en.wikipedia.org/wiki/Calque . Especially interesting is the typology of calques the author provides.
A related term in language learning is Interlanguage fossilization:
Interlanguage fossilization is when people learning a second language keep taking rules from their native language and incorrectly applying them to the second language they are learning. This results in a language system that different from both the person's native language and second language.