I have written previously about the difficulty of translation and localization. Appropriate translation/localization of works to another language can be a surprisingly difficult and arduous job. However, sometimes companies go too far, for several possible reasons, and just botch the whole thing to unacceptable levels.
Translating something to another language, from a purist point of view, is to reflect in the target language as accurately as possible what was said in the original language. The more closely the translation matches in meaning the original, the better. And, rather obviously, absolutely nothing of the original should be added or removed, unless it's absolutely necessary and there is no other option. (In some rare cases it may be outright impossible to translate something accurately, and conveying the exact meaning would require extensive amounts of ancillary explanations, which may be completely unsuitable for most media.)
Purists, who want an accurate translation, do not want anything changed, even if it's something that's completely exclusive to the original language or its culture. You often see this in fan translations of Japanese anime, often with even highly obscure terms and expressions left intact, and sometimes even lengthy translator explanations describing their meaning.
Most often, however, exact translations are pretty much exclusive to legal texts, contracts, and other similar formal documents, where accuracy, and conveying the meaning as accurately as possible, is of the utmost importance.
Most works, however, cannot afford this luxury. If you are, for example, dubbing a movie or cartoon made in another language, you only have so much flexibility to explain things (which is usually none at all). Even if you are subtitling such a work, there's still only limited amount of space you can use for explanations (and, in most works, due to convention, only what is said is subtitled, with no translator notes, save for very rare exceptions.) Translating a book may offer more flexibility, because with books a footnote is much easier and more natural. Thus books may offer a better chance at more accurate translations; however, even then this is not done very often, at least not with books of fiction, unless the accurate translation is somehow crucial to the plot.
For this reason translations of most works of fiction resort to localization. This means that things that do not translate well, or do not have a literal translation, are changed to something that people of the target audience will understand better.
The mildest form of localization happens when translating things like sayings and wordplay. A literal translation usually wouldn't make much sense, so the closest equivalent in the target language is usually used instead. (As an example, the English expression "kick the bucket" would probably not convey the same meaning to almost any other language if translated literally. Thus translations to other languages will change it to a local equivalent; or if there is no equivalent expression, then just a direct non-euphemism.)
Of course sometimes even in these mildest cases the translators may face some difficulty. Assume this conversation between two characters:
Person A: "Unfortunately he kicked the bucket."
Person B: "Why did he do that? Did he hurt his foot?"
This kind of wordplay can be extraordinarily difficult to localize to many languages, and translators often have to resort to very inventive workarounds, to keep the conversation fluent. In some cases they might even have to resort to changing the conversation completely, leaving nothing of the original joke in it at all, and inventing their own. An extremely lazy translator might just opt for a literal translation, but that would be just amazingly lazy and bad.
Of course even when localizing a work, the translator should try to keep as faithful as possible to the original, and make changes only when it's absolutely necessary, rather than spuriously.
But then, there are the botched localizations. The localizations where radical changes are made that cannot be justified with a simple "the literal translation wouldn't work in the target language". Things may be cut. Things may be changed for reasons other than fluency and understandability, such as political or cultural reasons. In some cases the translators may have a patronizing attitude towards their audience (ie. of the kind "they wouldn't understand this; let's change it or remove it completely".) Sometimes there may even be outright censorship, because the translator thinks that something is inappropriate, or would cause protest in the target audience.
And sometimes radical changes are done for no discernible reason at all. Sometimes it feels like the translator completely changed something just for the sake of it, even though the original was perfectly fine, and would have had a perfectly good translation that didn't even need localizing. Maybe the translator felt like wanting to introduce his own footprint into the work, or something.
Especially in the 80's and the early 90's this mentality sometimes went to absolutely ridiculous extents. For example the producer and writer Carl Macek became infamous for taking Japanese anime series, and completely re-cutting them and replacing the entire storyline and dialogue to something completely different. Sometimes he even took two different series and used pieces of footage from both, and merged them into a story (that usually had nothing to do with either original.)
In less extreme, but equally obnoxious cases, something that to some extent happens to this day, translators may still re-cut the original work and radically change the dialogue, even to the point of changing the story. In some cases people feel that the intent is to remove even the semblance of the original culture (eg. Japanese culture) and completely westernize the work. Whenever there is any mention of something that's particular to the original culture, it's replaced with a westernized version, them sometimes even going so far as to replace the images on screen. And, of course, they will freely cut anything that they don't like, with complete disregard to preserving the original work.
In some cases it's not that extreme, but can still be hilariously bad. For example one company that localized the Pokémon anime series to the United States went the extra mile to remove any references to Japanese culture from the series. The result was often ridiculous, hilarious, and obnoxious. Such as the infamous scenes where they replaced Japanese rice balls with "donuts" and "sandwiches", even going so far as to overlay the original images with their own versions. Because, you know, American kids have no idea what a rice ball is, and would probably be very upset about it. Or something. And heaven forbid they get curious about it. We aren't trying to teach them anything here!
Nowadays the biggest source of grievance with botched translations happens mostly with video games, especially those made in Japan. Things are changed, cut and censored. And sometimes the changes are completely nonsensical, and do not have any reason to exist (because there was nothing difficult or objectionable about the original text.)
There was a period in the mid-to-late-2000's where translator companies actually started caring about accuracy, and preserving the original work as much as possible. However, nowadays it seems that botched translations are making somewhat of a resurgence, probably caused by social justice warriors. Translators are becoming afraid of offending the 0.1% of the population that's most vocal about such things (and which by and large doesn't even consist of gamers.) Thus the remaining 99.9% of the population has to suffer because of them.