Hi bachew, here is someone speaking Russian as his native language, German on the native speaker level, English on a pretty decent level. I also can read and understand spoken Romanian, read in French, Portuguese and Polish and lead a meaningful discussion about old Indo-European languages like Old English, Old High German, Latin and Old Slavic languages. I also used to work as an interpreter and every now and then work as a translator. Besides, I taught my Romanian girlfriend Russian, a language that is typologically quite similar to Pali. My intention is not to boast how cool I am (well, not 100 % at least), I just wanted to show that I know what I am talking about.
In my experience, when it comes to highly synthetic languages like Old Indo-European ones, Russian or Baltic languages, the first thing one should do is to learn the grammar. By saying it, I don’t mean merely getting familiar with grammatical categories like tenses, cases or degrees of comparison, but really doing literally hundreds if not thousands of boring declension and conjugation exercises till you can conjugate or produce grammatical forms of any given word without giving it any thinking at all, it should become a fully automated process. It is not an organic process and it is pretty hard to achieve while watching movies or talking to people, since grammatical forms do not have a meaning on their own, and the only thing you practice when doing it is learning how to build these forms.But in a highly synthetic flexive language like Pali it is of crucial importance. Learning the vocabulary or idiomatic uses of grammatical forms is, on the contrary, a pretty organic process that you can and should enhance by the contact with the raw language material like books, movies, listening to people speaking in the public transport, etc.
This is where we start facing great difficulties. First, Pali is a dead language, it is not used as a native language by anyone. It means we can never be 100 % sure even about how correct our pronunciation of it is. On the other hand, it is a productive dead language, new texts in Pali were created even as late as the 19th century. As any dead productive language (Latin, Sanskrit, Old Church Slavonic, Classical Arabic) it was and is subject to linguistic interference with the native languages of people writing in it or speaking it. The Mediaeval Latin is pretty different from the language of Caesar and Cicero in grammar, pronunciation, and crucially in the vocabulary and idiomatic uses of grammar forms. Look at the Hebrew language: it had been dead for nearly two thousand years when it was adopted as the official language of Israel after small groups of enthusiasts started using it as their everyday language. However, there is not a single person who will tell you the Modern Hebrew and Ancient Hebrew are one and the same language, because they aren’t.
From all the above it follows that if you start using Pali as a spoken language you will likely not be speaking Canonic Pali but rather some language form we may conventionally call Modern Pali. For example, a native English speaker is not very likely to be using in his eveyday speech contructions like ‘having developed the right insight, you achieve liberation’ (interestingly, these constructions are pretty frequent in Russian, so a Russian speaker presumably wouldn’t have much problems with it making ‘mistakes’ in other areas of the Pali grammar). The same should be to a more limited degree true for the Commentaries by Buddhagosa, as they were written about 700 years later after the compilation of the bulk of the Pali Canon and must inevitably bear signs of linguistic inteference.
Therefore, if you want to learn Classical Latin of Caesar and Cicero, you will have little to no choice but to read texts by Caesar and Cicero, occasionally having a peak at graffiti from Pompeii to get an idea what the more colloquial language was like. The same is true for the Pali Canon. If you want to get an idea of the idiomatic use of grammar and / or vocabulary units at the time of the compilation of the Canon, you have no other choice but to read the Canon. Alternatively, if you just want to speak Pali no matter what, just like Zionist enthusiasts wanted to speak Hebrew in the 19th century, you can try to learn it as you learn English or German, but you should be aware that the result will most likely be (probably very) unsimilar to the Pali used in the Canon.