Saraiki language ?
Code map entry was added for skr-arab, so the request is fulfilled.
Saraiki has multiple scripts, but for now only the Arabic script is supported (and it may/should be the default if there's no script specified, unless another script is enabled like for Chinese or Serbian with their two script variants, causing the code without the script specifier to become deprecated/disused for translations, while still allowing a single portal to present these variants).
User categories may or may not specify their script variant in their Babelbox, so there are different categories ("skr" containing "skr-arab" as a subcategory). We don't know if and when another script variant will be enabled for that language (this will depend on community demand and support).
Note also that Saraiki is itself a member of another macro-language, with its own code in ISO 639 and BCP 47 (see Portal:Lah : Lahnda, لاهندا), and also using Arabic as its default script for all its existing member languages (but some of them also have script variants), because this script is now the most frequently found script for the modern usage of these languages (but this does not mean that other scripts are no longer used, there may exist minorities still using those variants, or other scripts for expatriated minorities that now live in other countries where another script is dominant and taught in schools). That's not exceptional and exists in fact for many languages (including English, which also uses in some cases the Deseret, Braille and SingWriting scripts, in addition to the dominant Latin script).
Saraiki in present day is written with its adaptation of the Perso-Arabic script in a large majority of cases, and I find it quite unlikely that another script variant would be added for it. It is unusual that in Wikimedia it is split between skr and skr-arab, when this is not done anywhere else. It would be like having ur-arab, ar-arab, sd-arab, and so on. The Saraiki alphabet uses letters which don't exist in any other Arabic based alphabet anyway, so it is sort of misleading to say it uses the same script. ٻ, ݙ for example are Saraiki representations of geminate consonants, in Punjabi we can only write these as بّ or ڈّ.
Don't confuse Saraiki, Lanhda, Urdu, and Punjabi, they are different languages with their own ISO 639-1 or ISO 639-3 codes.
All language codes can optionally be followed by a ISO 15924 script code ("-arab") to make distinctions when they can be written in multiple scripts. This is the case of Saraiki even if the Arabic script is now the most widely used for that language (this is also the case for Punjabi, and for Urdu, except that Urdu got its own language code separated from Hindi whose default script is Devanagari; and there's no need to specify the script for Hindi and Urdu which respectively use by default the Arabic and Devanagari script; but lot of authors agree that Urdu and Hindi are largely the same language "Hindustani" with minor dialectal differences).
However Saraiki is clearly distinguished from Punjabi because there are too many difference in the modern language (independantly of the script(s) used to write them)
Lahnda is not a language, it is a misattrubution of Lehndi, which is how the western dialect continuum of Punjabi is described. (Lahnda is grammatically masculine, Lehndi is feminine; we would say Lahnda Punjab but Lehndi Punjabi as languages in Punjabi/Saraiki are feminine.)
Saraiki forms a mutually intelligible continuum with Punjabi, the primary differences are phonetic rather than grammatical. (Saraiki does not have lexical tone.) I use the Saraiki translations to help with Punjabi translations; people who can read one can read the other. The difference in vocabulary is about as different as Spanish and Portuguese (that is mostly the same with some different pronunciations and inflections). Not every Saraiki speaker is even aware of the term Saraiki; they would just say they speak Punjabi as there is no clear line where one language begins and the other starts. Indian speakers of Lehndi dialects of Punjabi do not call it Saraiki even if they use the same language (they might say Multani, an older name).
Script codes are not used for Punjabi, we use pnb for Shahmukhi (Perso-Arabic) and pa for Gurmukhi.
Urdu and Hindi are indeed the same language; they are formal registers of Hindustani. However, for Urdu in particular, it arguably functions as a formal register for Hindustani and Punjabi. What I mean by this, is that in common understanding, when Punjabi speakers write in the language, they would be more likely to describe it as "writing Urdu" than "writing Punjabi with Shahmukhi script." Further, Punjabi is the most spoken native language of Pakistan, while Urdu is a lingua franca/trade language spoken natively by few. (This is a situation of diglossia, where the two languages co-occur in most instances.) Most users of Urdu speak Punjabi natively, and so mainstream Urdu has effectively become "Urdu with a Punjabi accent," or similar grammatical tendencies with an affected replacement of vocabulary; hence these lines are often blurred.