$$ echo -e "كاندي\ncat" | perl -Mutf8 -ne 'print if /^[{Script=Arabic}]+$/'
cat

s{
    (?=  [\p{Arabic}\p{Cyrillic}] )
         [\p{Arabic}\p{Cyrillic}\p{Common}\p{Inherited}] +
    (?<= [\p{Arabic}\p{Cyrillic}] )
}{}xg

$ uniprops -ga 627
U+0627 ‹ا› \N{ARABIC LETTER ALEF}
    \w \pL \p{Lo}
    All Any Alnum Alpha Alphabetic Arab Arabic Assigned InArabic Is_Arabic ID_Continue Is_IDC
       L Lo Gr_Base Grapheme_Base Graph GrBase IDC ID_Start IDS Letter Other_Letter Print Word
       XID_Continue XIDC XID_Start XIDS X_POSIX_Alnum X_POSIX_Alpha X_POSIX_Graph
       X_POSIX_Print X_POSIX_Word
    Age=1.1 Age=V1_1 Script=Arabic Block=Arabic Bidi_Class=AL Bidi_Class=Arabic_Letter BC=AL
       Canonical_Combining_Class=0 Canonical_Combining_Class=Not_Reordered CCC=NR

Bidi_Class=AL
Bidi_Class=Arabic_Letter
Bidi_Class=AN
Bidi_Class=Arabic_Number
BC=AL
BC=AN
Bidi_Class=B
Bidi_Class=Paragraph_Separator
Bidi_Class=BN
Bidi_Class=Boundary_Neutral
BC=BN
Bidi_Class=Common_Separator
BC=CS
Bidi_Class=CS
Bidi_Class=EN
Bidi_Class=European_Number
Bidi_Class=ES
Bidi_Class=European_Separator
Bidi_Class=ET
Bidi_Class=European_Terminator
BC=EN
BC=ES
BC=ET
Bidi_Class=L
Bidi_Class=Left_To_Right
BC=L
Bidi_Class=Left_To_Right_Embedding
BC=LRE
Bidi_Class=Left_To_Right_Override
BC=LRO