But then when you’re talking about 10:00 hours without specifying anything else, it actually means something completely different in the local context, apart from it being the exact same time globally. It doesn’t tell you whether it’s night or day at the other persons location. Your default point of reference in that system is the world, while even today, time is mostly used in a local context for most people. When I’m talking to someone abroad and I say “my cat woke me up at 5:00 in the morning”, I expect the other person to get the meaning of that, because the other person understands my local context.
When planning meetings you’d have to now the offset either way, because I’m not going to meet at idiotic times if there is an overlap in working hours between the two countries, which is something that you’d have to look up regardless of the time system. And if I send out a digital invite to someone abroad, the time zone information is already encoded inside it, and it shows up correctly in the other person’s agenda without the need to use a global time. In that sense UTC already is the global time and the local context is already an offset to that in the current system. We just don’t use UTC in our daily language.
But if it helps: I do agree that in an alternative universe the time system could’ve worked like that and it would have functioned. I just don’t see it as a better alternative. It’s the same complexity repackaged and with its own unique downsides.
Using English is the only way that all my colleagues are able to read it, but if it’s just meant for you, or only for Spanish speaking people, I’d say why not.