A rental system in two languages — where most SaaS breaks

The question lands in my inbox every month: "My customers are 60% Dutch and 40% Spanish — or English — which rental system do I pick?" The honest answer is that the well-known SaaS tools struggle with this, and the consequences never make it onto a product page. This post explains why, and what it costs to do it properly.

The problem nobody puts on a product page

"Multilingual" sounds like a checkbox: flip the interface to NL or ES and you're done. In practice, an international rental business runs four language rails in parallel, and all four have to be right:

1. The booking confirmation — the Dutch customer wants a Dutch email, the Spanish customer a Spanish one. Not just the text, but the date format, the greeting, the tone.
2. The invoice — the NL customer gets an invoice with BTW; the ES customer gets one with IVA, in Spanish, with the correct fiscal fields for the Spanish tax authority. Two tax regimes, two templates, the right one selected automatically based on the customer's country.
3. The rental contract / check-in instructions — two languages again, with legal text that's correct per country.
4. The admin — you want it in your own native language, regardless of which customer you're booking in right now.

Four rails. With SaaS built for one market, one of them works — and you handle the other three manually, with side documents, or not at all. Every booking, again.

Where Tommy, Booqable and Avantio break

None of these tools are bad. They were just built with one market as the starting point:

• Tommy — Dutch-market tool, point-of-sale first. ES templates are missing at the crucial moments (invoice, contract). Fine for a Dutch campsite with a small rental corner; not for international rental. (More: Tommy alternative.)
• Booqable — supports product-text translation, but the checkout flow and document templates are barely configurable. You can translate the words, not configure the whole customer journey per language. (More: Booqable vs custom.)
• Avantio — Spanish-market tool, strong from ~20 units up. NL is an afterthought: the Dutch customer and Dutch accounting are not the main case.

In all three cases you can make it work — with workarounds. And every workaround is a place where things break the moment the portfolio grows or a new employee takes over.

What a bilingual custom system does differently

A rental system built bilingual from the start does this fundamentally differently:

• Translation on every customer-visible string — including the PDF templates for invoices and contracts, not just the website copy.
• Locale per customer in the database — not "whatever the browser says," but "this customer communicates in Spanish" as a stored property. The next email is correct immediately.
• Two BTW/IVA rails in parallel — automatic selection of the right tax regime and invoice template based on the customer's country. No manual corrections after the fact.
• One admin in your native language — you work in Dutch (or Spanish, or English), regardless of which customer you're booking. The software adapts to you, not the other way around.

This isn't a feature you "switch on." It's a design choice you make from the first line of code — and that's exactly why off-the-shelf SaaS so rarely gets it right.

Concrete: what it costs and what it returns

The cost. A bilingual custom rental booking system runs €895/mo (the Rental Panel), everything included — build, hosting, monitoring, and ongoing development. First working version within four weeks, no separate project invoices, cancel monthly with a data export — no annual contract. NL and ES as equal rails (contract, portal, emails, invoices with both BTW and IVA) is standard at that price.

What it returns. Compared to SaaS where you handle the second language manually: no more side documents, no accounting corrections after the fact, and — often underestimated — no lost conversions from Spanish customers who bail on a Dutch booking form they only half understand. That last item doesn't show up on any invoice, but for a rental business with 40% international customers it's real money.

When it fits, and when it doesn't

This kind of system fits when:

• You actively serve customers in two language markets (not "we get the occasional foreigner")
• The four rails above are causing real friction — manual invoice corrections, customers confused by emails, time lost translating contracts per booking
• You have around 10+ units, or the volume justifies €895/mo

It doesn't fit when:

• Your second language is 5% of bookings and a short English email at checkout solves it
• You're under five units and Booqable on a basic plan covers you
• You don't actually do your own invoicing in two regimes (an accountant handles it offline and that works fine)

I'd rather tell you that upfront than sell you something you don't need.

Where I come in

This bilingual scenario — a rental business operating in both the Netherlands and Spain — is exactly what I specialise in. I work from the Costa Brava, build systems that treat NL and ES as equal rails, and know the fiscal and cultural context of both markets. One person, direct contact, fixed monthly price.

Want to know if your situation fits? Send me how you do it now — honest answer within a day, no pitch deck. Or have a look at the Rental page and the Caravanverhuurspanje case: a Dutch rental business on the Costa Brava that made exactly this step.