To use the English patch on a PS Vita, you must have a soft-modded console (custom firmware like HENkaku). Game Version : You need the Japanese version of Monster Hunter Frontier Z updated to version 1.99 Repatch plugin

For Vita owners specifically, the game was a technical marvel. It was one of the few online multiplayer games on the handheld that supported cross-play with the PlayStation 3 version, offering a robust online experience that the Vita library sorely lacked. When the servers went dark in December 2020, the game became unplayable legally, leaving behind only the memories of exclusive content that Western hunters never got to touch.

If you want, I can:

Six months later, a final patch emerged: Frontier G: Eternal Lone Wolf . It contained all 99 HR levels, the weapon style system, and even the mythical “Supremacy Species” fights—all offline, all in English. Leo never monetized it. He never took credit. He simply left a readme file in the download:

Enable English-speaking players to fully enjoy Monster Hunter Frontier G on PS Vita (and optionally on PS Vita TV / Adrenaline / emulation) with minimal original Japanese required.

Got that Monster Hunter Frontier running again : r/VitaPiracy