English will work fine, but then any language will work fine, as other answers have explained. The fact that English is closer than anything else, with Mandarin as the only real competition, means you might as well start there.
But I think your real problem is that you're thinking too much of enforcement:
… enforced a single global language for: education, legal documents, announcements, and for communication between citizens across the various states and even planets.
I think this is not only unnecessary, but counterproductive.1 You do need to teach everyone L2 English, but you don't need English-only education. And you need to allow people to use English when dealing with even local government, business contracts, etc., but I don't think you want to enforce it.
In fact, I think supporting local cultures and languages is not just something to grudgingly allow, but the potential key to a global language taking off.
Look at Europe today. What happens when a Swede is in Prague and meets an Italian? They communicate in English. In fact, they may each even do more communicating with the locals in English than by pulling out phrase books or translators to try to speak Czech. If you have a wide range of (unintelligible) local languages, and people traveling widely among them, all you need is for all of them to have a shared L2 language, and they'll use that language.2 How do you get that kind of travel? Obviously you need EU-style freedom-of-movement laws, and various things like prosperity, vacation time, transport infrastructure that you already want anyway. But having distinct local cultures also helps here. People like to go places that have different cuisine, unique historic sites, or even just different attitudes to late-night clubbing. Without any of that, nobody in Europe would bother going anywhere but Spain and Greece on vacation.
The same thing works in business. If two Italians want to do business, they do it in Italian. If an Italian and Swede want to do business… well, they could hire expensive interpreters, and then hire bilingual lawyers to check everything over after the fact, but it's easier to just do business in English. In fact, in fields like tech and banking, there are even companies that operate mostly in English instead of in their local languages, because it's worth trying to attract the best people in the world instead of the best people in your town.
You want people to absorb enough hegemonic culture that they keep up their L2 English instead of forgetting it after school. But just supporting language communities of around 5-50M people seems to already do that. That's enough people to have a native entertainment industry, but not one so big that it can make people ignore English entertainment. It's enough that high-profile programs can be professionally dubbed, but nowhere near everything that anyone want to watch. It's big enough to get people talking about those subtitled shows in their native language, but small enough that fans have to go to the international internet to really be involved in fandom.
As pointed out by Celestial Dragon Emperor in the comments, higher education is also very handy. If you make it reasonably cheap and easy for anyone who qualifies to go far from home for university, the best universities will soon all be teaching primarily in English, and soon most universities will, without being forced. (I believe this is exactly what's happened in India over the few generations since independence.)
The only real problem is how you deal with Chinese, Russian, and Spanish. Those language communities are large enough that people can arguably get enough travel, entertainment, and business without knowing English.3 But you're talking about "planets", so maybe that will take care of itself.
1. I'm assuming you don't want a highly centralized and repressive government, and that you mean what you later say about "supports local cultures and languages".
2. A couple centuries ago, if a Swede and an Italian met in Prague, they'd communicate in French. What's different today is that travel and L2 English are ubiquitous for commoners, in the way travel and L2 French were ubiquitous only for aristocrats.
3. Just encouraging local languages will help. As will modernizing orthography. If Hokkien and Cantonese speakers don't share hanzi spellings for their distinct languages, don't share L2 Mandarin, and do share L2 English, they'll start speaking English with each other. But that still leaves hundreds of millions of people with L1 Mandarin, L1 Russian, and L1 Spanish, which is still too many.