Response to my request has been very good, and quite a number of new languages got a localized summary for the interwiki bot. Still there are some remarkable exceptions, Japanese and Chinese for example still use English.
The current situation is:
Local summaries are used in the following languages: af,ar,be,be-x-old,br,ca,cs,csb,da,de,el,en,eo,es,eu,fa,fi,fr,fur,he,hr,hu,ia,id,is,it,ka,ksh,lmo lt,mzn,nds,nds-nl,nl,nn,no,os,pl,pms,pt,ro,ru,sk,sl,sr,su,sv,tet,tg,uk,vi,vo
The English version is used for: aa, ab, ak, am, ang, arc, as, az, ba, bg, bh, bi, bm, bn, bo, bpy, cbk-zam, cdo, ce, ch, cho, chr, chy, cr, cu, cy, diq, dv, dz, ee, en, et, ff, fiu-vro, fj, fo, ga, gd, got, gu, gv, ha, hak, haw, hi, ho, hz, ig, ii, ik, ilo, iu, ja, jbo, kg, ki, kj, kl, km, kn, ko, kr, ks, kv, kw, la, lg, lv, mg, mh, mi, ml, mn, mr, mt, mus, my, na, ne, new, ng, nv, ny, om, or, pa, pam, pdc, pi, pih, ps, rmy, rn, rw, sa, sco, sd, sg, si, simple, sm, sn, sq, ss, st, sw, ta, te, th, ti, tn, to, tpi, tr, ts, tum, tw, ty, ug, ur, uz, ve, wo, wuu, xh, yo, za, zh, zh-classical, zh-cn, zh-min-nan, zh-tw, zh-yue, zu
Arabic is also used for: ku,so German is also used for: als,bar,hsb,lb Esperanto is also used for: io,nov Spanish is also used for: an,ast,ay,ceb,gl,gn,lad,nah,pag,qu,tl,war Farsi is also used for: glk French is also used for: co,frp,ht,ie,kab,ln,lo,nrm,oc,wa Hebrew is also used for: yi Croatian is also used for: bs,mk,sh Indonesian is also used for: bug,jv,map-bms,ms Italian is also used for: eml,lij,nap,rm,roa-tara,sc,scn,vec Lithuanian is also used for: bat-smg Dutch is also used for: fy,li,pap,vls,zea Norse (bokmal) is also used for: se Romanian is also used for: roa-rup Russian is also used for: av,bxr,cv,hy,kk,ky,lbe,ru-sib,tk,tt,udm,xal