Canada's national air traffic control system is implemented in ~1 million lines of almost pure Ada, handling everything from the radars to the user interface.

Canada's national air traffic control system is implemented in ~1 million lines of almost pure Ada, handling everything from the radars to the user interface. If non-C-family isn't a dealbreaker I would seriously consider Ada for a large project. Very strong typing and modularity that are very suited for large-scale development, a wide range of available toolchains, but without the kitchen sink. (But I'm not qualified to make such decisions.) Besides, something like implementation language is almost never why a very large software project fails. (Though if you're already failing, then e.g. implementing your cloud service in COBOL is probably not helping.) It's usually from mismanagement, or a failure to define or understand the problem appropriately.