The dev's guide to localisation
Software that feels at home
in every country
Plurals, dates, money, names, addresses and right to left layouts. Hello World shows you what changes from place to place, why it breaks your code, and how to get it right in any language or framework.
The book is nearly here. Get 7 free lessons by email in the meantime, and hear the moment it launches.
By Liam Hammett
en-GB · London
British English
Hello World
- Price
- £1,234.50
- Date
- 6 July 2026
- Short date
- 06/07/2026
- Number
- 1,234,567.89
- Time
- 18:30
Localisation is more than translation.
It's every assumption your software makes
about the people using it.
Share of websites
Share of internet users
- English
- 49.5% 25.9%
- Chinese
- 1.3% 19.4%
- Arabic
- 0.6% 5.2%
Sources: W3Techs and Internet World Stats. Read chapter 1.
Fix the bugs you can't see from home
Imagine you've shipped this checkout, and now it needs to work for people in other regions. What could go wrong? Change its language to find out, then fix each issue the way the book teaches. The field guide collects every one the book covers, country by country.
Issues
Bugs to fix
- Turn on JavaScript to hunt the bugs.
Seven parts, from first principles to launch day
Every chapter stands on its own, so you can read it front to back or jump to the problem in front of you. Each one ends with a checklist and further reading.
- Part 1 Foundations
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What localisation is, how locales work, how to work out who your user is, and why text is harder than it looks.
- Part 2 Words
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How languages differ, translating your interface, messages that change shape, working with translators, and why English is not one language.
- Part 3 Numbers, money, time and place
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Number formats, units, phone numbers, currencies, calendars, dates and timezones, addresses, people's names and everything else forms ask for.
- Part 4 Design
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Text that changes length, fonts that can't draw every character, pictures that need localising too, and designing for right-to-left languages.
- Part 5 Beyond the web page
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Emails, jobs, PDFs and APIs, native mobile and desktop apps, and AI features that have to work in every language.
- Part 6 Shipping it
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URLs and SEO, the networks, devices and services your users actually have, testing, keeping it working after launch, and running localisation as a business.
- Part 7 Putting it together
-
A step-by-step playbook for localising a new or existing app, and the master checklist.
Hand the checklists to your agent
Plus comes with 11 skills for Claude Code and other agents that read skills. They follow the same rules as the book, and each one points back to the chapters behind it.
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/internationalise-audit
Audits a codebase for everything the book covers, and reports each problem with its file, line and the chapter to read.
-
/internationalise
Makes an app translatable and locale-aware, one phase of the playbook at a time.
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/localise
Gets an internationalised app ready for one region: formats, currency, tax, addresses, layout and hreflang.
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/extract-translation-strings
Moves hardcoded text into your translation files as whole sentences with proper plurals.
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/pseudolocalise
Runs your app in a fake, longer, right-to-left language and reports what broke.
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/rtl-check
Reads your code and reports what will break in Arabic, Hebrew, Persian and Urdu.
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/timezone-review
Follows dates and times from input to storage, display, jobs and emails, and reports where they change meaning.
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/form-review
Reviews one form end to end and proposes what it should ask in each country you serve.
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/check-translations
Checks translation files against the source language: missing and extra keys, placeholders dropped or renamed, broken ICU syntax, the wrong plural forms for the language, strings left in English, text likely to clip, and punctuation that doesn't suit the locale.
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/translator-brief
Drafts a translator brief, glossary and style guide for one locale from your codebase and product, using the book's templates.
-
/l10n-vocabulary
The book's glossary as a reference your agent can use, so you can both name things precisely.
Pay once, keep every update
Start with Basic and upgrade to Plus any time for the difference. If it isn't for you, you get a full refund within 30 days.
Basic
$49
Regular price $74
Early-access price. It goes up when the video course comes out.
- The whole book on the web
- The PDF, in colour and printer-friendly
- Lifetime updates
Available at launch
Plus
$99
Regular price $149
Early-access price. It goes up when the video course comes out.
- Everything in Basic
- The AI skills for your coding agent
- The templates
- The video course, when it comes out
Available at launch
“Our website, they told us, was full of typos.”
Liam Hammett
Author of Hello World
When Helm Tickets expanded into the US, American event organisers told support the site was full of typos. It wasn't. A UK company had spelled "organiser" with an S, and fixing it turned into an overhaul that had very little to do with spelling.
Liam Hammett has been building localised websites and apps for well over a decade, from ticketing to Future's English language editions across eight regions. Today, Liam works at Geocodio, where addresses from every country show how differently the world works.
Read the prefaceBefore you start reading
Who is Hello World for?
Developers building software for people in more than one country, and the designers, product managers and translators who work next to them. You don't need any localisation experience to start.
Do I need to use a particular language or framework?
No. Each chapter explains the idea first, then shows it in code. Most examples are JavaScript and PHP, with HTML, CSS, SQL, Swift and Kotlin where they help, and every idea maps onto the tools you already use.
Isn't localisation just translation?
Translation is one part of it. The book also covers dates and timezones, numbers and money, names, addresses, forms, layout, right to left design, URLs and SEO, testing, and running localisation as part of a business.
Can I read some of it first?
Yes. The preface, chapter 1 and chapter 5 are free to read in full, with no account needed, and every other chapter shows its opening. You can also get 7 free lessons by email.
What formats does it come in?
The whole book on the web, plus a colour PDF and a second PDF made for printing.
Will it get updates?
Yes, for life. New chapters and fixes land on the web and in the PDF, and the changelog lists every one.
Can I buy it for my team?
Yes. Buy a seat for everyone doing the work and hand the seats out by email. Larger teams get a discount, and when someone leaves, their seat can go to someone else.
Start with 7 free lessons by email
One short lesson each morning, each on a localisation bug that's cheap to avoid and expensive to fix later. You'll also hear the moment the book launches. Unsubscribe any time.