Ship delta differences may mean bugs found in one code base are too late to fix in the other. Synergy is lost between code bases. Data interoperability among languages is seldom thought through. File format interchange is probably not considered between major language differences, such as Japanese and Greek, or maybe not even among similar languages, such as French, English, and German. In this model, the product has no code forks.
Single source is developed by one product group for all anticipated targets.
Binary size can be optimized for major language regions, without resorting to completely separate teams and separate source. Code not required by all users is conditionally compiled out, based on geographic target. Less duplication of head count by having one group accountable for a worldwide enabled product. Those bugs can be reported once and fixed once. Ship deltas reduced to time lag for actual translation, instead of being subject to engineering delays.