Consequently putting the doubts relating to whether the adoption of an international language is possible for the moment, assuming that the adoption of such a language is decided by out own will and no significant mistakes are made in the section of that language, it is believed that everyone would agree that one wouldn’t able to talk about the harm of an international language even in the slightest.
I have had a crack at this below - it’s a pretty confusing sentence! I am totally open to corrections etc
The core sentence is:
したがって、「。。。」国際語の害悪についてかりそめにも口に出せないことに誰しも同意するはずだ。Therefore, […] everyone should agree that there could be no talk, even in jest, about the harm of an international language.
The middle three clauses:
国際語の採用が可能かどうかに関する疑問はしばらく脇において
…putting aside for a moment the question of whether it would be possible for an international language to be accepted…
そういう言語の採用が我々の意志によって決まり
…the adoption of such a language would be determined by our will…
その言語の選択に大した間違いを犯さないと仮定した場合
…assuming that you do not make a mistake in selecting the language…
So, I would probably go for something along these lines:
Therefore, putting aside for a moment the question of whether it would be possible for an international language to be accepted, the adoption of which would be determined by our will, and assuming no grave mistake is made in the selection of the language, everyone ought to agree that there could be no talk, even in jest, about the harm of an international language.
