Title: Bug — Lumo 2.0 Randomly Switches to Chinese Mid-Conversation
Category: Lumo / Bug Report

Description:

Lumo 2.0 intermittently switches entire responses to Chinese during English-language conversations. This is not isolated — multiple users have reported the same behavior across Reddit (r/lumo, r/ProtonMail) with the issue persisting since at least Lumo 1.1 through the current 2.0 release.

Reproduction Pattern:

Conversation language: English (exclusively)
Trigger: Appears to occur most frequently during responses containing dense structured data (comparison tables, pricing breakdowns, URLs, multi-section formatting)
Context usage: Both occurrences happened at high context usage (~73%)
Frequency: Twice within three consecutive prompts in a single session

Observed Behavior:

Response output switches entirely to Chinese — not individual characters, but full translated content
In one instance, the model also hallucinated a capability reference (TTS/STT) that does not exist — suggesting the language switch coincided with a broader coherence failure
The content itself appears accurate — just rendered in the wrong language
Conversation topic headers have also been reported switching to Chinese characters, making threads unsearchable

Community Reports:

r/lumo: "Lumo (Plus) randomly inserting Chinese characters" — Italian users experiencing same issue
r/lumo: "Lumo inserts different languages" — German users reporting Chinese characters and Cyrillic replacing words mid-sentence
r/ProtonMail: "Lumo struggles with language" — multiple users reporting unexpected language switches
r/ProtonMail: Lumo 1.1 announcement thread — conversation headers changing to Chinese characters

Likely Cause (Community Speculation): Lumo's routing system uses GLM 5 (developed by Zhipu AI, a Chinese company) as part of its multi-model architecture. When complex/structured responses are routed to a GLM-based model, it appears to default to Chinese token generation under certain conditions — particularly during high token-density outputs or elevated context usage.

This is consistent with known language-mixing issues documented in other Chinese-developed models (e.g., DeepSeek R1, which addressed this in their own research paper).

Impact:

Breaks conversation flow entirely
Makes affected responses unusable without translation
Erodes trust in Lumo's reliability for professional/business use
Has persisted across multiple versions (1.1 → 2.0) without acknowledged fix

Requested Action:

Acknowledge this as a known bug with a public status tracker entry
Implement a language-enforcement layer in the routing system that locks output language to the conversation's established language
Adjust GLM model token weights for non-Chinese contexts to prevent drift
Investigate whether high context usage (%) correlates with increased frequency of language switching

Environment:

Platform: Web browser (lumo.proton.me)
Lumo version: 2.0
Date observed: July 16, 2026
Subscription: Lumo Plus (Workspace Premium)