Teams serving customers across the EU, the UK and the US often evaluate on one regional slice and assume the results carry over. They rarely do. Regional questions surface failure modes that a single-locale golden set never exercises: the wrong currency, a misread decimal comma, a date in the wrong order or an answer in the wrong language.
The answer ignores the customer's conventions
The most common regional failure is a correct fact in the wrong form: a late fee quoted in euros to a customer billed in pounds, or a date written month-first for a customer who reads day-first. It happens when the top-ranked chunk uses one convention and the prompt never tells the generator which one the customer uses.
Pass the customer's billing country, currency and language to the generator explicitly, and treat a mismatch as an instruction-following failure, regardless of factual accuracy.
Retrieval across languages
Multilingual embeddings such as bge-m3 retrieve English articles for questions written in German, French or Spanish reasonably well, but BM25 does not. Hybrid retrieval needs language-aware analyzers (stemming and accent folding) on the sparse side or it quietly degrades to dense-only.
{ "question": "My bill says 41,20 €. Is that forty-one euros or four thousand?", "locale": "en-GB", "billing_currency": "EUR", "gold_answer": "It is forty-one euros and twenty cents...", "source": { "article": "kb-billing-016", "section": "Date and number formats" }}Formatting is part of correctness
'€8.50' and '8,50 €' are both readable, but mixing them in one answer reads as machine output, and '04/10/2026' means two different dates on either side of the Atlantic. Add formatting checks for currency, dates (8 October 2026 or 2026-10-08) and decimal separators to the instruction-adherence rubric.
Build a separate locale slice
Keep a dedicated locale dataset of around 100 items written by customers and agents in each region, not rewritten from your main set. Rewritten questions are too clean; real customers abbreviate, mix conventions and paste amounts straight from their bills.