Upvote:3
My mother in law was denied a UK visa in part because she did not translate her bank statements. They say that documents not in English or Welsh must be accompanied by a translation, and they mean it. That the documents would be costly to translate does not have any bearing on this requirement.
For your own cost-benefit analysis, weigh the cost of translating the documents against the cost of submitting an application that will almost certainly be refused. Throwing away your application fees is also costly.