Since languages degrees are generally somewhat unpopular in the UK fewer people apply to them so it's relatively "easier" to get into those courses, even at quite good universities. While nothing is guaranteed I think meeting the requirements (or being predicted to meet them) while applying to an undersubscribed course like that gives a very good chance of getting a conditional offer. Of course, one needs to actually meet those requirements by the end of the school year to be able to matriculate

And yes the UK system is very different to the US system. Since students in the UK don't have a "rolling" GPA from their classes in school (their results are determined by external public exams like A-levels, GCSEs etc), and since the exams form which their grades do derive aren't held until after applying, unis in the UK do normally make those conditional offers on the basis of
predicted grades.
Since there's a fair amount of uncertainty as a result most universities outside of Oxford and Cambridge realistically need to make more offers than they would anticipate having "places" for (although there are no formal restrictions on how many students unis can take outside of medicine and dentistry). Unisy know out of the number of offers they make, some will not accept choose to make it their "firm" or "insurance" offer at all (and thus decline it - you can only ultimately have 2 offers accepted in UCAS), they may make them their "insurance" choice and not their "firm" choice and if they achieve their grades will go to the other uni, some will not do as well in their exams and miss the offer and the uni may or may not feel they can accept them, some might meet their offer for the firm choice but decide not to matriculate/enrol in the end, etc. There are a lot of potential attrition points.
So really for modern languages I think usually meeting or being predicted to meet the standard entry requirements and writing a not-terrible personal statement (not necessarily outstanding) is probably going to be sufficient to be a serious contender if not get an offer.
In any event there's nothing to lose really! I suppose there's the ~£25 UCAS fee but since you have to pay that to apply through UCAS at all (regardless of which 5 unis you apply to) and it's very unlikely one would get 0/5 offers unless they completely didn't meet or couldn't meet the requirements, there's very little risk here in applying.