### The Problem

Using native Qt translation files (TS, `*.ts`) for exchanging with Transifex platform limits means to provide context
to translators to the only category:

| C++ source code                               | TS XML element                                 | Transifex metadata
|-----------------------------------------------|------------------------------------------------|:------------------:
| Class Name                                    | `<name>`ClassName`</name>`                     | Context
| `disambiguation` parameter of `tr()` function | `<comment>`Short comment`</comment>`           | N/A
| [Translator Comments](https://doc.qt.io/qt-5/i18n-source-translation.html#translator-comments) `//: ...` | `<extracomment>`Nice comment.`</extracomment>` | N/A

More details:
- https://docs.transifex.com/formats/introduction
- https://docs.transifex.com/formats/qt-ts
- https://doc.qt.io/qt-5/linguist-ts-file-format.html

### The Solution

[XLIFF](https://en.wikipedia.org/wiki/XLIFF) file format is supported by Transifex much better.

And Qt provides us with a stand-alone conversion tool `lconvert`.

```sh
$ lconvert -o bitcoin_es.xlf -i bitcoin_en.ts
```

Now more context options are available:

| TS XML element                                 | XLIFF XML element                               | Transifex metadata
|------------------------------------------------|-------------------------------------------------|:------------------:
| `<name>`ClassName`</name>`                     | `<group resname="ClassName">`...`</group>`      | yes
| `<comment>`Short comment`</comment>`           | `<context>`Short comment`</context>`            | yes
| `<extracomment>`Nice comment.`</extracomment>` | `<note from="developer">`Nice comment.`</note>` | yes

More details:
- https://docs.transifex.com/formats/xliff
- https://code.qt.io/cgit/qt/qttools.git/tree/src/linguist/lconvert/lconvert.pro?h=5.12.10

---

Looking for Concept (N)ACKs.
#include <QtGlobal>
#ifdef __GNUC__
#define UNUSED __attribute__((unused))
#else
#define UNUSED
#endif
static const char UNUSED *bitcoin_strings[] = {
QT_TRANSLATE_NOOP("bitcoin-core", "The %s developers"),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"%s corrupt. Try using the wallet tool bitcoin-wallet to salvage or restoring "
"a backup."),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"-maxtxfee is set very high! Fees this large could be paid on a single "
"transaction."),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"Cannot obtain a lock on data directory %s. %s is probably already running."),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"Cannot provide specific connections and have addrman find outgoing "
"connections at the same."),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"Cannot upgrade a non HD split wallet without upgrading to support pre split "
"keypool. Please use version 169900 or no version specified."),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"Distributed under the MIT software license, see the accompanying file %s or "
"%s"),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"Error reading %s! All keys read correctly, but transaction data or address "
"book entries might be missing or incorrect."),
QT_TRANSLATE_NOOP("bitcoin-core", ""
"Error: Listening for incoming connections failed (listen returned error %s)"),