Translated strings should not be used for NumberProperty units

[pixelzoom]

In BallNode.js:

    // Create the number display for the speed of the Ball, which appears above the ball. To be positioned later.
    const speedNumberDisplay = new PlayAreaNumberDisplay( ball.speedProperty, {
      visibleProperty: valuesVisibleProperty,
      valuePattern: StringUtils.fillIn( collisionLabStrings.pattern.vectorSymbolEqualsValueSpaceUnits, {
        symbol: collisionLabStrings.symbol.velocity,
        units: collisionLabStrings.units.metersPerSecond
      } )
    } );

    // Create the number display for the momentum of the Ball, which appears below the ball. To be positioned later.
    const momentumNumberDisplay = new PlayAreaNumberDisplay( ball.momentumMagnitudeProperty, {
      visibleProperty: valuesVisibleProperty,
      valuePattern: StringUtils.fillIn( collisionLabStrings.pattern.vectorSymbolEqualsValueSpaceUnits, {
        symbol: collisionLabStrings.symbol.momentum,
        units: collisionLabStrings.units.kilogramMetersPerSecond
      } )
    } );

Values for the units options to NumberDisplay must be in units.js. So the above will likely fail for anything other than English.

[pixelzoom]

Fixed in the above commit. @jonathanolson please review.

[jonathanolson]

Looks good to me, thanks!