Localized and ephemeral replies using Discord.JS?

I've recently been playing a lot with localization on my Discord Bot, and I was wondering something.

When using localization, you can create a reply that uses different languages based of the user's language settings.

As seen in the code here :

client.on(Events.InteractionCreate, interaction => {
	const locales = {
		pl: 'Witaj Świecie!',
		de: 'Hallo Welt!',
	};
	interaction.reply(locales[interaction.locale] ?? 'Hello World (default is english)');
});

My problem is that I would like to do the same thing except using the ephemeral parameter, like so:

await interaction.followUp({ content: 'Pong !', ephemeral: true });

But when I try to mix the two :

async execute(interaction) {
    const locales = {
    	pl: 'Witaj Świecie!',
	de: 'Hallo Welt!',
    };
    await interaction.reply(locales[interaction.locale] ?? 'Hello World!', ephemeral: true);
});

It doesn't work since the way you're supposed to write an ephemeral answer is like this:

await interaction.followUp({ content: 'Pong again!', ephemeral: true });

So I was wondering if anyone had an idea, on how I could make the reply localized and ephemeral, and maybe change up my code so that it works.

That would be super helpful, thanks!

You were pretty close, you just need to add your content as the value of content:

await interaction.reply({
  content: locales[interaction.locale] ?? 'Hello World!',
  ephemeral: true,
});

Your first example works because reply accepts a string as the content of the message.

// ✅ works
interaction.reply(locales[interaction.locale] ?? 'Hello World (default is English)');

The second one doesn't work because you still pass a string as the first argument but if you want to use ephemeral messages, you need to pass an object instead of that string with a content and an ephemeral key.

// ⛔️ doesn't work
await interaction.reply(
  locales[interaction.locale] ?? 'Hello World!',
  ephemeral: true
);

// ✅ works
await interaction.reply({
  content: locales[interaction.locale] ?? 'Hello World!',
  ephemeral: true,
});