How I can display a menu with spellcheck suggestions?

Upon your code the issue resides upon:

for error in self.spellingerrors:
   for suggestion in error.replacements:
       self.menu.addcommand(suggestion)

The reason ehy is because there's no callback to trigger upon the action once clicked. The minimum fix you can do is:

for error in self.spellingerrors:
   for suggestion in error.replacements:
      self.menu.addcommand(label=suggestion,command=lambda s=suggestion: self.applysuggestion(s))

Then place this method:

    def applysuggestion(self, text):
        self.delete(0, tk.END)
        self.insert(0, text)
        self.spellingerrors.clear()
        self.configure(highlightbackground="gray")

import tkinter as tk
import languagetoolpython
class SpellCheckEntry(tk.Entry):
    def init(self, master=None, pureenglish:bool=False, kwargs):
        self.var = tk.StringVar()
        super().init(master, textvariable=self.var, kwargs)
        language = "enUS" if pureenglish else "auto"
        print(language)
        self.tool = languagetoolpython.LanguageTool(language)
        self.spellingerrors=[]
        self.menu = tk.Menu(self, tearoff=0)
        self.bind("", self.showsuggestions)
    def spellcheck(self,text):
        matches = self.tool.check(text)
        self.menu.delete(0, tk.END)
        self.spellingerrors=[]
        for m in matches:
            if("ELGR" in (m.ruleid) or "ENUS" in (m.ruleid)):
                self.spellingerrors.append(m)
                print("Matching Rule",m.ruleid)
        if self.spellingerrors:
            self.configure(highlightbackground="red", highlightcolor="red")
            for error in self.spellingerrors:
                for suggestion in error.replacements:
                    # FIX: Placing a callback here
                    self.menu.addcommand(
                        label=suggestion,
                        command=lambda s=suggestion: self.applysuggestion(s)
                    )
        else:
            self.configure(highlightbackground="gray")
        return self.spellingerrors
    #FIX: Callback that applies data upon input 
    def applysuggestion(self, text):
        self.delete(0, tk.END)
        self.insert(0, text)
        self.spellingerrors.clear()
        self.configure(highlightbackground="gray")
    def showsuggestions(self,event):
        try:
            self.menu.tkpopup(event.xroot, event.yroot)
        finally:
            self.menu.grabrelease()
    def get(self):
        text = super().get().strip()
        errors = self.spellcheck(text)
        if errors:
            raise ValueError(f"Spelling errors detected: {text}")
        return text
def submit():
    try:
        value = entry.get()
        print("Valid text:", value)
    except ValueError as e:
        print(e)
root = tk.Tk()
root.title("SpellCheckEntry Demo")
root.geometry("400x150")
tk.Label(root, text="Type something:").pack(pady=5)
entry = SpellCheckEntry(root, pureenglish=True, width=40)
entry.pack(pady=5)
btn = tk.Button(root, text="Validate", command=submit)
btn.pack(pady=10)
root.mainloop()

Pay attention upon methods:

• spellcheck
• applysuggestion

Where I made these changes.

class SpellCheckEntry(PasteableEntry):
    def init(self, master=None, pureenglish: bool = False, kwargs):
        self.var = tk.StringVar()
        super().init(master, textvariable=self.var, kwargs)
        language = "enUS" if pureenglish else "auto"
        self.tool = languagetoolpython.LanguageTool(language)
        self.spellingerrors = []
        self.menu = tk.Menu(self, tearoff=0)
        self.bind("", self.showsuggestions)
    def spellcheck(self, text):
        matches = self.tool.check(text)
        self.menu.delete(0, tk.END)
        self.spellingerrors = []
        for m in matches:
            if "ELGR" in m.ruleid or "ENUS" in m.ruleid:
                self.spellingerrors.append(m)
        if self.spellingerrors:
            self.configure(highlightbackground="red", highlightcolor="red")
            for error in self.spellingerrors:
                for suggestion in error.replacements[:5]:
                    self.menu.addcommand(          # ← label= keyword
                        label=suggestion,
                        command=lambda s=suggestion, e=error: self.applysuggestion(e, s)
                    )
        else:
            self.configure(highlightbackground="gray")
        return self.spellingerrors
    def applysuggestion(self, error, suggestion):
        text = self.var.get()
        corrected = text[:error.offset] + suggestion + text[error.offset + error.errorLength:]
        self.var.set(corrected)
        self.configure(highlightbackground="gray")
    def showsuggestions(self, event):
        text = self.var.get().strip()
        self.spellcheck(text)             # ← run check before popup
        try:
            self.menu.tkpopup(event.xroot, event.yroot)
        finally:
            self.menu.grabrelease()
    def get(self):
        text = super().get().strip()
        errors = self.spellcheck(text)
        if errors:
            raise ValueError(f"Spelling errors detected: {text}")
        return text