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it is much easier to learn Bahasa Indonesia or spoken Japanese for an English speaker than it is to learn Russian

The United States government agencies that track this matter don't generally seem to think so. But if you have other evidence on this point, I'd be glad to hear it.

I agree in general that a grammatical feature such as minimal marking of nouns for case and verbs for person, number, or gender, making word order the main basis for grammar distinctions, makes Chinese eerily familiar for native speakers of English. But even though Chinese grammar is "easy" for native speakers of English, to the degree that some Americans say "Chinese has no grammar" (definitely a false statement), nonetheless lack of a lot of cognate vocabulary or similar phonological system usually means that the native speaker of English will thrive as a learner of any Indo-European language over almost any non-Indo-European language.

The comparisons I've seen most often assume native speakers of English learning various languages to an equal tested level of functional proficiency after government-sponsored training. Length of training to reach the required level is generally longer for the non-Indo-European languages than for the Indo-European languages. The "easy" languages for English speakers are the typically studied languages like French, German, and Spanish, perhaps because of prior exposure as well as close similarity. It would be interesting to see what studies of language learning starting from various native languages to acquire various target languages are showing these days.