Automatic translation/interoperability between programming languages. The fragmentation of software into dozens of major languages hurts software quality, limit

Automatic translation/interoperability between programming languages. The fragmentation of software into dozens of major languages hurts software quality, limits language choices, limits adoption of new languages, limits availability of software on new/less popular platforms, increases cognitive load for developers and sysadmins... (and JavaScript as the most popular transpiler target today is depressing)