Among the constructed languages that I have seen, I believe that Interlingua was the closest to how a language that could replace English as the international language should be.

I disagree with some grammatical choices made for Interlingua, but in any case it had a simple grammar and the vocabulary was well chosen among the words that are common to the greatest number of European languages. Thus I could read and understand Interlingua without knowing anything about it before that.

Interlingua has a vocabulary bias towards Romance languages, but that is due to the fact that Romance words, mostly coming from Latin or French, are also widespread in English, and also in other language groups like Germanic or Slavic, while much less Germanic or Slavic words are found in languages from other groups. Therefore when selecting the words that are found in most European languages, there are more Romance words than from the other groups.

Esperanto being created by L.L. Zamenhof ... a Polish Ashkenazi Jew. Full circle!