See: https://www.proz.com/kudoz/dutch-to-english/law-general/7185322-artikel-311bis.html

Latin               in English (following Marijke Singer / JurLex / EU English Style Guide)
Article 1 bis Article 1a
Article 1 ter Article 1b
Article 1 quater Article 1c
Article 1 quinquies Article 1d
Article 1 sexties Article 1e
Article 1 septies Article 1f
Article 1 octies Article 1g
Article 1 nonies Article 1h
Article 1 decies Article 1i
Article 1 undecies Article 1j
Article 1 duodecies Article 1k
Article 1 terdecies Article 1l
Article 1 quaterdecies Article 1m
Article 1 quindecies Article 1n
Article 1 sex[ties]decies Article 1o
Article 1 septdecies Article 1p
Article 1 octodecies Article 1q
Article 1 novodecies Article 1r
Article 1 vicies Article 1s
Article 1 unvicies Article 1t
Article 1 duovicies Article 1u
Article 1 tervicies Article 1v
Article 1 quatervicies Article 1w
Article 1 quinvicies Article 1x
Article 1 sex[ties]vicies Article 1y
Article 1 septvicies Article 1z

JurLex

artikel 3 bis = Article 3a

Van Dale

nummer 3 en nummer 3 bis = No 3 and No 3b
artikel 65 bis = section 65b

Proz question re how to translate "bis" (in Dutch to English texts)

Marijke Singer: 

Since there will always be debate on this, I tend to select one style guide and stick to it. I use the EU English Style Guide (which you can download):

A reference such as Article 198a is not to a subdivision but to an article subsequently inserted after Article 198. In English, the letter is always in lower case and closed up to the number. In some languages, such articles are numbered Article 1 bis (ter, quater, quinquies, etc.). When translating, use the English form. (For national legislation, see 23.15.)

Article 1 bis
Article 1 ter
Article 1 quater
Article 1 quinquies
Article 1 sexties
Article 1 septies
Article 1 octies
Article 1 nonies
Article 1 decies
Article 1 undecies
Article 1 duodecies
Article 1 terdecies
Article 1 quaterdecies
Article 1 quindecies
Article 1 sex[ties]decies
Article 1 septdecies
Article 1 octodecies
Article 1 novodecies
Article 1 vicies
Article 1 unvicies
Article 1 duovicies
Article 1 tervicies
Article 1 quatervicies
Article 1 quinvicies
Article 1 sex[ties]vicies
Article 1 septvicies
 
are:

Article 1a
Article 1b
Article 1c
Article 1d
Article 1e
Article 1f
Article 1g
Article 1h
Article 1i
Article 1j
Article 1k
Article 1l
Article 1m
Article 1n
Article 1o
Article 1p
Article 1q
Article 1r
Article 1s
Article 1t
Article 1u
Article 1v
Article 1w
Article 1x
Article 1y
Article 1z

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philgoddard:

Much to my surprise, we've never had this in Dutch to English, though it's been discussed to death in French to English. I hope you won't mind my giving a reference in another language pair!

https://www.proz.com/kudoz/french-to-english/law-general/5872490-article-l-19-bis.html

It's confusing to translate this as 'a' or 'b' just because this numbering convention doesn't exist in English.

artikel 311bis =
article 311 bis

(https://www.proz.com/kudoz/dutch-to-english/law-general/7185322-artikel-311bis.html)

Whether numbering convention exists in English

Michael Beijer:

on the debate as to whether this system of inserting stuff exists in English, I just found the following. Not quite the same context but fairly similar.

"3.8.3 Where ordinal numbers are used for a list of conditions (first, second, third etc) it is not obvious what to call a new condition that needs to be inserted into the middle of the list in future. The use of cardinal numbers (1, 2, 3 etc) or letters (A, B, C etc) is preferable. Future conditions can then be added as 1A, 2A, 3A or AA, BA, CA etc."

(https://www.gov.uk/government/publications/drafting-bills-for-parliament/2024-03-19-drafting-guidance )

References