From Civilization V Wiki
This page contains any known limitations of the modding framework. To clarify, the difference between a limitation versus an issue is that the issue was unintentional and that a fix is expected in the near term. Limitations may not have been directly intended but are not considered requiring immediate attention. Many limitations will be removed in the future as planned feature updates happen.
Discussion of these limitations should take place on the associated talk page ('discussion' link at the top of the page). To add a new limitation, create a new section by using the new section link ('+' link next to 'edit' at the top of the page).
Presently, mods are not activated during multiplayer games. This is only considered an initial limitation and will be addressed in a future patch.
DLL modding is currently not supported. A future patch will be coming later this year or early next year which will remove this limitation.
It is not possible to install a language pack via Mod Browser and expect the new language to appear in written languages drop down box once the language pack mod is enabled. A Mod game must be started for this to work, adding an extra step at the start of the game.
It is possible to make a language pack and place it to My Games\Sid Meier's Civilization 5\Text by replacing Language_en_US tags.
Steam controls the official languages via it's own language tab page in game properties dialog. The selected language will be downloaded & installed while the unselected are uninstalled.
Note: this is not officially confirmed by Firaxis.
Buildings cannot produce resources
There is no known way to make a building produce a resource (strategic or otherwise), as opposed to consuming it. There have been unconfirmed reports of this being worked around, but the person who claimed to have done it did not respond to requests for further information.
It's possible that it might be worked around with event-driven Lua, but no-one has identified suitable events. It would be better for the DB schema to be extended to allow for identification of resources produced, with a quantity (for strategic resources).
- UPDATE: There is a workaround for this, but it's a bit of a kludge - probably as elegant as it can get with the system as-is, though. A thread on CivFanatics for a modcomp by Whys covers it, but basically it works by, every turn, checking (for every player, including AI, every building) if any building is in the list of buildings that add resources; it then checks if they were there last turn, and if they were it ignores them; it then adds the relevant resources, updates the list from last turn, and so on. I haven't read the Lua too closely, but it presumably also checks the list for last turn to see if any have been lost, etc.