The ECB stipulates that the nominative singular should be written "euro" in all languages (taking account of different alphabets, such as Greek).
Current usage by the ECB and the Commission is to use the plural form "euros" (with "s", non-capitalized). This is recommended by the two relevant style guides, the Interinstitutional style guide and the Translation Directorate style guide.
The style guide of the European Commission Directorate-General for Translation currently says:
20.8 The euro. Like ‘pound’, ‘dollar’ or any other currency name in English, the word ‘euro’ is written in lower case with no initial capital and, where appropriate, takes the plural ‘s’ (as does ‘cent’):This book costs ten euros and fifty cents. However, in documents and tables where monetary amounts figure largely,make maximum use of the € symbol (closed up to the figure) or the abbreviation EUR before the amount.
The Interinstitutional style guide, (7.3.3. Rules for expressing monetary units http://publications.europa.eu/code/en/en-3703...
) currently has a caveat:
"The text in point 7.3.3 is in draft form and is currently being analysed by the institutions. When it has been finalised you will be notified on the News page of this website." but has the following note (using "euros" in the plural):
When a monetary unit is referred to generally but an amount is not included, it is written in letters, except in tables (see ‘When to use the ISO code (EUR)’):
an amount in euros
a sum in pounds sterlingPrior to 2006
, I understand (as quoted elsewhere), the Translation style guide (20.7) had:
"Guidelines on the use of the euro, issued via the Secretariat-General, state that the plurals of both ‘euro’ and ‘cent’ are to be written without ‘s’ in English. Do this when amending or referring to legal texts that themselves observe this rule. However, in all other texts, especially documents intended for the general public, use the natural plurals ‘euros’ and ‘cents’ "
and according to the old version
of the Interinstitutional style guide (7.3.1):
"In English, the terms euro and cent are invariable (no plural 's'), notwithstanding the acknowledgement in a footnote that ‘The spellingwithout an “s” may be seen as departing from usual English practice for currencies’. Notwithstanding that in Italian, German and Greek the words ‘euro’ and ‘cent’ are also used in their plural-less form, in most other languages, including French and Spanish, the name of the single currency tends to vary in the plural, both inofficial and in everyday use."