Translate the Loanwords, Too

A subtrope of Blind Idiot Translation and a relative of Recursive Translation. This is when a work in one language uses a word from another language, but when the work is translated into the language which it borrowed that word from, the translators are thrown off and try to translate it (even though it's already in their language) instead of leaving it as is. There are a few possible outcomes;

In the case of loanwords, they might remain untranslated even if they're used differently in the work's original language.
The phrase might be reworded either because the translator fails to realise that its a word from their language or is determined to translate every part of the script whether necessary or not.
If the word is a loanword or has roots in another language entirely (for example French phrases like "coup de grace" or Greek and Latin suffixes like "phobia" are both used in English often enough to be treated as a part of the language) then it's translated from that (for example phobia becomes "fears" and "coup de grace" becomes "blow of mercy"). This makes even less sense than the above, as it requires that the translator realise they're dealing with a word that's supposed to be foreign.
The company translators are paid by how much work is needed to make something work for the new audience. By claiming such unneeded things are required, they get paid more.
Finally (and possibly more benevolently), the translator might translate words in the original script which are in the language being translated into the language of the original script to Keep It Foreign or just apply a Translation Correction if the script's original implementation of the translator's language was badly done. Alternately, the loanwords might be translated into yet another language, especially if they were being used as a Gratuitous Foreign Language alternate to common terms in the original language.

When someone demands something be translated from a language they speak anyway it's Completely Unnecessary Translator, if they simply took something in the original language that would be too rude for native speakers it's Tactful Translation, if the "same" language actually does need translating it's Separated by a Common Language. "El Niño" Is Spanish for "The Nino" is the inverse; when a phrase from the first language is left untranslated because it's a loanword in the second.

Examples of Translate the Loanwords, Too include:

Anime and Manga

Some fansubs of the Soul Eater anime translate "Arachnophobia" (the name of the antagonists' organisation) from the Japanese script into "Fear of spiders" or "Fear of Arachne".
A small one shows up in The Melancholy of Haruhi Suzumiya. In one scene Kyon says a few words in Japanese, then in English. In the dub and some subs he does the opposite.
Parodied in Excel Saga: At one point there's an English text scroll, so there are Japanese subtitles. The English version then provides a hilariously inaccurate translation of those subtitles.
There is a fansub of Yu-Gi-Oh! which humorously translates duro/draw (as in draw a card) as "pick."
The "Ripoff Church" from Black Lagoon was translated as the "Church of Violence" in several fansubs. The official subs (and dub) keep the name intact.
An infamous case in the original Tokyo Pop translation of the Sailor Moon manga, which wasn't about a single word, but an entire English poem by Yeats. The poem was translated back into English without recognizing that it was originally an English poem. This was fixed in later releases.
The translators who worked on Mega Man NT Warrior somehow managed to mistranslate half the Gratuitous English. Not only was it in English to begin with, but the first two Mega Man Battle Network games had already been released in English without any of the same errors. Yet somehow, many instances of "punch" became "thump", and many a "bomb" became a "boomer".

Eastern Animation

Adventures of Captain Vrungel used "obviously Bowdlerized dub" gag (see above), including "cretino!" dubbed as "untranslatable wordplay".

Literature

Jorge Luis Borges initially named one of the volumes of his collected works with the English The Maker, which he then translated into Spanish as El hacedor. The first English translators were unaware of Borge's intentions, and were unsure how to translate "hacedor" (which can mean either "maker" or "doer"), so they just sidestepped it and named the book Dreamtigers (after one of the stories from the book).
In Twenty Thousand Leagues Under the Sea, Professor Aronnax recalls an expedition to the Nebraska badlands, which he gives in the original French as les mauvaises terres du Nebraska. Some English translators have failed to recognise the term, resulting in translations like "the disagreeable territory of Nebraska".
In the short story "The Chief Designer", Russian spacecraft names usually left in Russian when being discussed in English (Vostok, Mir) are translated into English as well ("The East", "The Peace").

Toys

A subset of Transformers fans, particularly prior to 2000 or so, was fervent about referring to characters by their "Japanese" names when talking about Japanese G1 series. You know, where the leader was actually "Comboi", not that crazy "Convoy" term other fans would use when talking about Optimus Prime's Japanese name. Another notable one is insisting on using "Minelba" instead of "Minerva".

Web Original

The Other Wiki does occasionally; for example, their article on Metal Gear Solid 3: Snake Eater gives the Japanese "name" in katakana, and then romanizes it to "Metaru Gia Soriddo Suri Suneku Ita".
IMDb has similar issues sometimes.
- It used to be far worse, but has been cleaned up considerably in the past few years.. yet there are still the likes of "Bîsuto uôzu chô seimeitai Toransufômâ supesharu" or rather "Beast Wars chô seimeitai Transformers Special".
This quote from X-Play reviewing Gladiator the game:

Young Augustus Ceasar (thinking): "'Et tu, Brute...' And you, Brutus...."
Morgan: "That's right: He's translating Latin -- to himself!"

Fansubs often do this because of the Gratuitous English trope and the fact that many loanwords aren't used by the borrower in the same manner as in the original language. Chances are, you've probably never heard 'diamond' shortened to 'dia,' ice cream merely called 'ice,' or a two-person team called a 'combi' if you're a native English speaker. There are even terms that are not immediately recognizable as English (such as portmanteaus of two words' katakana spellings. Dekotora = decorated truck.)

Real Life

Brazilian former president Fernando Henrique Cardoso saw fit to explain to an English speaker interviewing him what French loanword "malaise" meant. All of that in a horrible pronunciation of English.