Example in other direction:
URL in Lemma [[de:Olympische Sommerspiele 1912/Tennis/Dameneinzel/Halle]]: http://www.itftennis.com/procircuit/tournaments/women%27s-tournament/info.aspx?tournamentid=1020000015 (with %27!)

Test with original URL with %27: Spezial:LinkSearch/http://www.itftennis.com/procircuit/tournaments/women%27s-tournament/info.aspx?tournamentid=1020000015 =>fail/no match

Test with manipulated URL with >'<: Spezial:LinkSearch/http://www.itftennis.com/procircuit/tournaments/women's-tournament/info.aspx?tournamentid=1020000015 =>success/[[de:Olympische Sommerspiele 1912/Tennis/Dameneinzel/Halle]]

Valid URL-encoded chars should not be replaced by decoded chars.

Here a list of all replaced encoded chars:

[%21 !], [%24 $], [%26 &], [%27 '], [%28 (], [%29 )], [%2A *], [%2B +], [%2C 0], [%2D -], [%2E .], [%30 0], [%31 1], [%32 2], [%33 3], [%34 4], [%35 5], [%36 6], [%37 7], [%38 8], [%39 9], [%3A :], [%3B ;], [%3D =], [%40 @], [%41 A], [%42 B], [%43 C], [%44 D], [%45 E], [%46 F], [%47 G], [%48 H], [%49 I], [%4A J], [%4B K], [%4C L], [%4D M], [%4E N], [%4F O], [%50 P], [%51 Q], [%52 R], [%53 S], [%54 T], [%55 U], [%56 V], [%57 W], [%58 X], [%59 Y], [%5A Z], [%5F _], [%61 a], [%62 b], [%63 c], [%64 d], [%65 e], [%66 f], [%67 g], [%68 h], [%69 i], [%6A j], [%6B k], [%6C l], [%6D m], [%6E n], [%6F o], [%70 p], [%71 q], [%72 r], [%73 s], [%74 t], [%75 u], [%76 v], [%77 w], [%78 x], [%79 y], [%7A z], [%7E ~]

you will find the URL-decoded chars only in externalurl table, the URL in html of the articles is the original URL (with encoded chars).

Here an other example, with regular utf-8 char whitch get encoded:

Original-URL: https://web.archive.org/web/20150627045239/http://www.hedenstedif.dk/nyheder/senior/senior-2015/scholz-er-fast-mand-hos-standard-liège/

LinkSearch with original-URL: fail
LinkSearch with https://web.archive.org/web/20150627045239/http://www.hedenstedif.dk/nyheder/senior/senior-2015/scholz-er-fast-mand-hos-standard-li%C3%A8ge/ => success / [[:de:Alexander Scholz]]

Change 275906 had a related patch set uploaded (by Ferveo):
Normalize user provided URL link for Special:LinkSearch page

https://gerrit.wikimedia.org/r/275906

• Please evaluate if it is possible to give the original URLwithout changes into the el_from column (but do not html escapes into it) and the normalized URL into the el_index columne. This could also help to find internationalized domain names (IDN rfc5890)

• For %27 please normalize »'« to %27 because »''« ist part of wikitext syntax.

Change 275906 merged by jenkins-bot:
Normalize user provided URL link for Special:LinkSearch page

https://gerrit.wikimedia.org/r/275906

Example for broken URL

Original URL (fount in [[de:Kurt Heinrich (Psychiater)]]):
http://www.landtag.nrw.de/portal/WWW/Webmaster/GB_II/II.2/Suche/Landtag_Intern/Suchergebnisse_Landtag_Intern.jsp;jsessionid=5B5A4AE8211733D1E9FA082AD9A520E9?w=native%28%27+%28+ID+ph+like+%27%27LI720620%27%27++%29+and+%281=1%29%27%29&order=native%28%27ID%281%29%2FDescend+%27%29&view=detail

Broken LinkSearch output:
http://www.landtag.nrw.de/portal/WWW/Webmaster/GB_II/II.2/Suche/Landtag_Intern/Suchergebnisse_Landtag_Intern.jsp;jsessionid=D4FB3ED8A8129CC36F1571848FC9072A?w=native('+(+ID+ph+like+''LI861220''++)+and+(1=1)')&order=native('ID(1)/Descend+')&view=detail

LinkSearch
https://de.wikipedia.org/w/index.php?target=http%3A%2F%2Fwww.landtag.nrw.de%2Fportal%2FWWW%2FWebmaster%2FGB_II%2FII.2%2FSuche%2FLandtag_Intern%2FSuchergebnisse_Landtag_Intern.jsp&title=Spezial%3AWeblinksuche

If a User takes LinkSearch Output and C&P it into wiktext like this: [http://www.landtag.nrw.de/portal/WWW/Webmaster/GB_II/II.2/Suche/Landtag_Intern/Suchergebnisse_Landtag_Intern.jsp;jsessionid=D4FB3ED8A8129CC36F1571848FC9072A?w=native('+(+ID+ph+like+''LI861220''++)+and+(1=1)')&order=native('ID(1)/Descend+')&view=detail $$Linktext$$]
the result URL will brake at »''«

@ferveo: Hi! Is this task still valid and should still be open? If yes, are you still working (or still plan to work) on this task? (If you do not plan to work on this task anymore, please remove yourself as assignee (via Add Action... → Assign / Claim in the dropdown menu) so in theory others could work on it.) Thanks!