All that glitters is not gold nor do any identical letters make for identical languages. The confusion is not between Spanish and Italian or German and Dutch, languages that evolved sufficiently long ago so as to be immediately distinguishable, but instead between languages that are directly related by history but have only recently (in historical terms) gone different ways.
One example is French from France as compared to that written in Quebec. Clearly, the letters and grammar are identical as are most of the words. However, a deeper analysis would identify some traps for the unsuspecting translator. On the one hand, Quebecois tends to more firmly insist on French roots as compared to English roots in business, e.g., réunion and planification instead of the free French use of meeting and planning. On the other hand, funny Americanisms, such a chien chaud for hot dog, do show up. On a lexical note, French-Canadian meanings can differ, including déjeuner and dîner are breakfast and lunch, respectively, in Quebec as compared to the Parisian petit déjeuner and déjeuner. For more information see https://www.technitrad.com/the-differences-between-french-and-canadian-french-when-translating-professional-documents/ Both customers and translators should confirm the source of the French text.
Hebrew and Yiddish share the same letters but have different vocabulary sources. Hebrew uses roots derived from Hebrew and Aramaic with some more recent English and Russian additions. On a humorous note, I just heard a music judge say “lejamjem”, meaning to have a jam session. By contrast, Yiddish is a localized combination of Hebrew, Russian, Polish and German roots, transliterated into Hebrew applying Yiddish grammar. It was the language that allowed Jews from all over Eastern Europe and Russia to communicate with each other. Clients see the Hebrew letters and assume that the text is in Hebrew. While a non-Yiddish speaker can understand some of the text, it is a language in itself.
My personal bugaboo is Ukrainian. I translate many certificates from Russian and occasionally don’t pay attention to the entire text when quoting. Only upon started the job do I discover that the months of the year are different. Curiously enough, the Ukrainians use a much older system of month names based on agriculture and plants, naming each month for that feature of it. For example, travyen means grass and is the equivalent of May while Syerpen means a sickle and is the equivalent to August. For a beautiful presentation of the Ukrainian calendar see https://www.ukrainianlessons.com/months/.This is only one of the differences in these two separate languages but it is easy to catch and helps me avoid having to find a Ukrainian translator. Not all Cyrillic languages are created equally.
In the most perfect of worlds, translators would always read the entire document carefully before proposing a price and accepting a job. In reality, there are occasional lapses. As Bregalad the Ent would say, they are occasionally "hasty" and don’t properly check the source text to identify the actual language, creating a solvable but avoidable problem. On the bright side, it does make for a funny story.
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Picture credit: Image by <a href="https://pixabay.com/users/thevirtualdenise-5804203/?utm_source=link-attribution&utm_medium=referral&utm_campaign=image&utm_content=2491047">Denise Husted</a> from <a href="https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=image&utm_content=2491047">Pixabay</a>