Maybe it's better to focus on smaller changes first. Like implementing a "special attack" mechanic by giving some units either passive or active special abilities.  These are even described on some documentation pages, but they're still not implemented. Perhaps the most famous is the ability of Hastati to throw pila at nearby enemies, before going into melee. 

That's exactly my point. Total War has its own features, its own mechanics. Code-wise, it is very different from Age of Empires and other RTS. You are giving the example of BFME2, which is both very different from Total War and very different from 0 A.D. in its mechanics.  Implementing charging bonus, morale, fatigue, ammo etc. do not require battle formations. It is actually the battle formations which require new features to make sense. All the mechanics in battle should make sense with the formations. It requires a holistic approach. The challenge is to produce a well rounded design and balanced mechanics based on battle formations. While keeping the other features and design of 0 A.D., notably on the economy.  And also making all that with the current engine, notably the pathfinding. This is a major overhaul. Total War and BFME2 were designed with this idea from the start, don't underestimate the ramifications. It would be great but I don't see how it is feasible with the current ressources and management.

That's a good description of when the message appears but I agree that using the word rejoin in a situation when the user joins the game for their first time is misleading. The game used to be translated using Transifex, but when I last tried to make an account there it was quite a pain.

0 A.D. is changing stereotypes!

Okay. Battalions seem like they could be a good idea, as long as they are OPTIONAL. Replacing individual unit training with battalions is not a good idea, but being able to turn a formation into a battalion (or a group of units into a battalion) seems like it would grant a lot of new features, while being unique.