CodeCompletion not execute after set language of LanguageTextField

The code doesn't compile. Please post the actual working snippet of your issue.
About missing completion, it might be that builtin JSON completion providers interfere here.

Full  demo code

import com.google.common.collect.Lists;
import com.intellij.icons.AllIcons;
import com.intellij.json.json5.Json5Language;
import com.intellij.openapi.project.Project;
import com.intellij.openapi.ui.DialogWrapper;
import com.intellij.ui.TextFieldWithAutoCompletion;
import com.intellij.util.textCompletion.TextCompletionUtil;
import org.jetbrains.annotations.Nullable;

import javax.swing.*;

public class DemoDialogWrapper extends DialogWrapper {
    private final Project project;

    public DemoDialogWrapper(@Nullable Project project) {
        super(project, false);
        this.project = project;
        init();
        setSize(400, 300);
        setTitle("demo");
    }


    @Override
    protected @Nullable JComponent createCenterPanel() {
        TextFieldWithAutoCompletion.StringsCompletionProvider completionProvider = new TextFieldWithAutoCompletion.StringsCompletionProvider(Lists.newArrayList("a", "b"), AllIcons.Nodes.Method);
        TextCompletionUtil.DocumentWithCompletionCreator documentWithCompletionCreator = new TextCompletionUtil.DocumentWithCompletionCreator(completionProvider, false, false);
        return new com.intellij.ui.LanguageTextField(com.intellij.json.json5.Json5Language.INSTANCE, project, "", documentWithCompletionCreator, false);
        
        //Change Json5Language.INSTANCE to com.intellij.openapi.fileTypes.PlainTextLanguage 
        //CodeCompletion works

    }
}