The MBROLA project web page provides diphone databases for many[1] spoken languages.
Due to its free usage only for non-commercial applications, MBROLA was as alternative choice for private/home users for de facto speech synthesis engine eSpeakNG in Linux workstations, but mostly was not used for commercial solutions (e.g. for speaking time clocks, boarding notifications for ports and terminals etc.)
On January 23, 2019, tool called MBROLATOR was released to provide creation of MBROLA database from WAV files with the same license.
Although it is diphone-based, the quality of MBROLA's synthesis is considered to be higher than that of most diphone synthesisers as it preprocesses the diphones imposing constant pitch and harmonic phases that enhances their concatenation while only slightly degrading their segmental quality.
MBROLA is a time-domain algorithm similar to PSOLA, which implies very low computational load at synthesis time.