Japanese pitch accent actually varies across regions. Some have no pitch accent at all! I think this shows that it's not very important unless you want to sound like a native speaker. I never bothered to learn the "standard" pitch accents but I tend to imitate the Kansai pitch accent of my wife :)

In Japan/ese, the pitch/stress thing is overrated, and so are regional language differences. When natives point it out to me, it strikes me a little more than cultural gatekeeping. Linguistic context matters much more. How often are you listening to your own native language and you are confused by two words that sounds similar (like 'hashi' in Japanese for bridge/chopsticks)? Almost never. Advice: Ignore it when natives that criticise your pronunciation. Ask them how is their German or Thai is... and they will freeze with shame.

Where I come from, to criticise a non-native speakers accent or small grammatical errors (that do not impact the meaning) is a not-so-subtle form of discrimination. As a result, I never do it. (To criticise myself, it tooks many, many years to see this about my home culture and stop doing it myself.) Still, many people ask me: "Hey, can you correct my <language X> when I speak it?" "Sure!" (but I never do.)

Sort of. Indonesian had Jawi, based on the Arabic script. People in today's Vietnam mostly wrote in Chinese AFAIK. Those methods of writing were dominant among the people who could write. But the populations were mostly illiterate, so it was easy for colonial administrators to supplant the existing writing systems with Latin as they introduced European-style schooling.

> No dominate written language at the time of European Colonialization

Vietnamese used to be written using Chinese orthography just like Japanese.

The French forcibly cracked down on this form of orthography, and following independence, later modernists attempting to copy Ataturk along with latent Sinophobia due to the Chinese colonial era meant this for of orthography has largely been relegated to ceremonial usage.

A similar thing happened with Bahasa Indonesia, as Indonesia's founding leadership was more secular and socialist in mindset compared to neighboring Malaysia where Jawi remained prominent because of the Islamist movement's role in Malaysian independence.