Some stuff can't be fixed on LibreOffice, let's try to list them and explain why.
convert_add function from "at" or "atm" to "Pa" gives same answer
tdf#72174 gives details but in brief, "at" and "atm" are 2 different units whereas LibreOffice consider them as same unit. This is due to 2 things:
- the will to be compatible with Excel which treats them as same unit too
- the fact that odf standard has followed this Excel's error
ODF standard should be fixed in its version 1.3 (https://issues.oasis-open.org/browse/OFFICE-3851)
Missing right parenthesis isn't detected in Basic
First a bug, tdf#80731, has been declared for this and it's been fixed. Then tdf#106529 has been declared because lots of macros suddenly triggered errors. Even if most of (all?) LibreOffice macros have been fixed for the missing right parenthesis, any extension or macro used in companies may trigger this error. So the initial fix has been removed.
From 6.4.0 missing right parenthesis will be detected if macro is opened in IDE. It would allow to stop creating buggy macros and allow tolerance for existing buggy running ones. (see https://cgit.freedesktop.org/libreoffice/core/commit/?id=d628258f279d003ba4e11f1f7e2e69273acd008c)
Some code refer to "Persistant" whereas right spelling is "Persistent". This can't be fixed because has been declared as public interface and thus would break API compatibility (see https://opengrok.libreoffice.org/xref/core/offapi/type_reference/offapi.idl#4315 and https://gerrit.libreoffice.org/#/c/35096/)
Update from 2021/04/29: Situation improved after this last commit: https://cgit.freedesktop.org/libreoffice/core/commit/?id=45779b685b8b1e75ce750bbb20b30cee8fd40851 "Replace "Persistant" by "Persistent"in WinClipboard (vcl/win) since now we have it in idl files with the historically wrong "Persistant" ..." and the commits indicated in the comment of this patch. So now "Persistent" can be used and "Persistant" is considered as deprecated.
Some code refer to "THROUGHT" whereas right spelling is "THROUGH". it's been fixed in 5.4 version and for the moment the wrong spelling has been deprecated, see https://cgit.freedesktop.org/libreoffice/core/commit/?id=8913353a8fd2a1d281c2d8a33ca795d97201b7bc
Mail merge config contains this typo. This can't be fixed because it would break compatibility (since it may be stored in LO profile).
"commited" instead of "committed" is used in "XTransactionListener" This can't be fixed because it would break published API.
Found in oox/source/drawingml/customshapes/presetShapeDefinitions.xml + oox/source/export/preset-definitions-to-shape-types.pl This can't be fixed because the typo is in the standard standard https://standards.iso.org/ittf/PubliclyAvailableStandards/c071691_ISO_IEC_29500-1_2016_Electronic_inserts.zip The preset definitions are in c071691_ISO_IEC_29500-1_2016_Electronic_inserts\OfficeOpenXML-DrawingMLGeometries.zip, file presetShapeDefinitions.xml
Wrong Spanish translation "SIFECHA" for "DATEDIF"
"DATEDIF" should have been translated to "FECHADIF". Since there's the mistake on Spanish Excel, we can't change it. See https://bugs.documentfoundation.org/show_bug.cgi?id=128126#c7
Wrong icons in conditional formatting
As tdf#126733 indicated, "the happy and sad faces are inverted for both the normal and colored sets of emoticons". According to comments from https://gerrit.libreoffice.org/c/core/+/97636, it'll bring some regression on existing documents. So even if tdf#126733 is right, we're stuck.
Typos on purpose for being compatible with old extensions
Some LO code take into account typos just for being compatible with old extensions which may use them and never updated. eg in sc/source/core/data/dptabsrc.cxx SC_SIMPLE_SERVICE_INFO_COMPAT( ScDPHierarchies, "ScDPHierarchies",
"com.sun.star.sheet.DataPilotSourceHierarchies", "com.sun.star.sheet.DataPilotSourceHierarcies" )
SC_SIMPLE_SERVICE_INFO_COMPAT( ScDPHierarchy, "ScDPHierarchy",
"com.sun.star.sheet.DataPilotSourceHierarchy", "com.sun.star.sheet.DataPilotSourceHierarcy" )
Since majority of people don't want to remove them because of these legacy extensions, we're stuck.
"isMutipleMode" instead of "isMultipleMode" is used in "XListBox" This can't be fixed because it would break published API.
"getSeletedPositionStart"/"getSeletedPositionEnd" instead of "getSelectedPositionStart"/"getSelectedPositionEnd" is used in "XAccessibleTextSelection" This can't be fixed because it would break published API.