After some experimenting, I think I have found the answer. When phone settings don't match any of the localization folders present in the .pkpass archive, Wallet uses the localization folder that comes first in the file order of the filesystem. Wallet seems to use the first localization folder delivered by libc's readdir function when run on the contents of the .pkpass. That function's manpage says: Note that the order of the directory entries vended by readdir() is not specified. Some filesystems may return entries in lexicographic sort order and others may not. So in the case of iPhone and its Wallet app, the order is determined by the APFS filesystem. It's based on filenames, but not alphabetical. An old FAQ explains, Calling readdir(2) on a directory in APFS returns filenames in hash order, where the hash consists of 22 bits of a CRC-32C hash of the null-terminated normalized filename in UTF-32, according to the APFS reference. In practical terms, the user gets a random localization when none of the locales in the pass is set as one of the preferred languages. The priority order of localizations (for a list of 144 localization codes) is: de, ur, he, en_AU, zh-Hant-TW, ar, el, zh-Hans, ja, fa, zh-TW, mr, el-GR, ms-MY, mk, sq, uk-UA, eu, en, it-IT, co, zh-Hant-HK, hi_IN, uk, es_419, da_DK, kab, gu, es_MX, ku, nb-NO, zh_CN, kn, nb, pa, ca-ES, en-GB, am, es, sw, is, sl, ru-RU, nl_NL, pt_BR, da, gl, es-419, et, it, sv_SE, bg, sk, kk, pt_PT, fr-CA, sat, tr-TR, es-ES, sr, ms, ar-SA, si, be, ta, ne, fr-FR, ml, ja-JP, sv, ko-KR, id-ID, te, cs, km, ko, vi-VN, fil, th_TH, an, zh-Hant, sc, my, uk_UA, no, fa-IR, ro-RO, hu, hr-HR, da-DK, hi-IN, zh_HK, ka, bn-IN, ga, tr, ast, pl, zh_TW, hu-HU, gu-IN, en_GB, br, pt-BR, brx, nl-NL, vi, lv, es-MX, lt, ru, cy, cs-CZ, nb_NO, zh-CN, af, sk-SK, de-DE, sl-SI, fr_CA, es_ES, fr, fi, id, nl, th, pl-PL, nn, pt, de-CH, as-IN, sv-SE, bn, pt-PT, oc, gl-ES, he-IL, ro, th-TH, wa, hr, hi, ca, gd Good luck finding a pattern in that.